So, I've noticed a lot of people who say stuff about how they don't have a lot of money for games. Well I spend a lot of time looking at indie games and stuff and quite a lot of them are free or in open beta.
Sooooooooo here we go. PC only, sorry Console players. As for Linux peeps (Which there are probably hardly any) good few of these are Linux games too 
#1 - OpenTTD - Open-Source version of Transport Tycoon 3, bit hard to figure out what to do but it's very fun. You get to build railway systems with the pretty cool signals for making it all work without your trains crashing (I have yet to figure out how to make a good one other than multiple train tracks each with 1 train which is sorta fool-proof but not that cool and not very space efficient.) and also you get to make airplanes and helicopters and bus stations and truck routes and all that jazz. Really fun, check it out. Windows, Linux and Mac
#2 - Ace of Spades - Like Minecraft and Digging? Like FPS? Perfect game for you. "Ace" of "Spades" is an FPS game where trench warfare and the like all happen naturally. You spawn in a destructibe world that the maps are usually player made. You have a spade (See the name makes sense now), some blocks, 3 grenades, and either an SMG, Rifle, or Shotgun. You can dig out the landscape and make tunnels, buildings, trenchs etc. Very fun little game that's free and has lots of players. 32 player servers. And who doesn't love digging all the way to under the enemies base to make a happy pink fun house underground and then get killed many times finishing up the very obvious entrance while also potentially giving access to your base to the other team cause you made a huge tunnel, though usually the game ends before you finish the place 
Windows only.
#3 - King Arthur's Gold - Ace of Spades sound interesting? Not like the FPS aspect? Take a look at KAG or King Arthur's Gold. This is a very fun game that has a free version and a buy version, if you buy the game you get extra modes like Zombie Defense. Pretty sure it's still in Alpha or Beta. Anyway - to the gameplay.
KAG is a 2d game, it looks a lot like Terraria. As much as Ace of Spades is the FPS Minecraft Clone, KAG is the 2d platformer, action, fighty whatever Terraria Clone. You can spawn as an Archer, Soldier, or Builder. The Archer has a bow and no Melee, you have to chop down some trees at the start to get arrows. They can also clime trees and snipe hidden from the tops which have leaves. Though your arrows usually get seen pretty quickly. People are not blind The Soldier has a sword and a shield, the shield can be used as a sort of parachute, to block, and you can swipe with the sword. The sword can be used as a quick swipe or you can charge up for a couple seconds for a more powerful one. The Melee combat could be pretty good but I never bothered learning it, cause of what the builder can do
The best part of this game for me is the builder. You can build buldings and towers out of stone and stuff, there are doors that only your team can get through (Remember, everything is destructible except for the maps indestructible parts in the ground) and also trap platforms that if the enemy tries to go on it they will fall through, usually on to placeable spikes that hurt everyone. I really love tunneling all the way to under the enemies base, and then there is the struggle of when they find out, being chased through the tunnel and having to block up the passage with stone. Pretty suspensful, especially when you can hear another tunneler nearby... Who could potentially bump into you with a few soldiers ready to burst out when the tunnel is finished. Hilarious fun when all you do is tunnel at least for me, and I'm sure the melee combat is great, a lot of people seem to like it. As the builder to build things you need wood and stone for the certain things. Buildings will collapse if you take out the bottom of them and it's quite spectacular. I was on a server once and all everyone was doing was building humongous ladders all the way to the tap that where suuuuper wide, then they'd knock it down and there would be an awesome huge collapse of ladders.
KAG is really fun, I play it every once in awhile when I'm bored, it's on Windows, Linux, and Mac so no one is left out. (Wow this is going to end up being a pretty long post...)
#4 - Tremulous - Tremulous is an FPS, but before you sulk away guys who didn't think Ace of Spades would be cool cause it was FPS there are some cool ideas here. If you've ever heard of Natural Selection or Natural Selection 2, and it looked interesting - get this game for a bit of an idea of what it's like sorta. Basically there are aliens are humans. The humans build bases around their reactor which if destroyed they lose. You can build turrets, tesla thingies, armories, spawn points, etc. You start with a medkit which is a 1 use heal over time thing (You can get a new one if you go on a healing station and once fully healed if you don't have one it gives you one) a blaster (Shitty unlimited ammo pistol), and Assault rifle, which is alright.
You can sell your assault rifle to buy a new gun from the armory (Took me awhile to realize this), and you can get the very deadly but horribly teamkill-tastic flamethrowers which are hazardous to everyones health, mass drivers which shoot a high damage shot sorta like a generic rifle weapon but more deadly, laser rifle which is a slower rate of fire more damage assault rifle kinda gun, the shotgun which is cheapest other than the free assault rifle but is kinda hard to use, the minigun which is pretty much the best weapon in the game as long as you have a battlesuit which is a large amount of armor. (Doesn't let you wear jetpacks though), the something something which shoots a big ball of radioactive yellow stuff which is most expensive and is incredibly high damage (Easy to hurt yourself though) and it's hard to use so only really the pros use it There are others, but those are just the ones I put as I thought of them.
Now to the aliens side. They also build bases (The base building isn't what you think, you have a defined space and you build defenses and stuff there, but it's still cool) but the aliens are much different and much harder to use. The original alien is a very small little guy who is very low health but has a deadly attack (Basically, bump into an unarmored guy 2 times and he's dead), very fast and hard to hit. They can crawl up walls so that makes it even harder to hit them (The view gets horizontal/upside down etc. so it can be disorientating especially at first) and they can ambush you from behind a doorway and such. They're very hard to use though, and if you are against a really good player who is one of these it's very hard, I was getting pwned by bots on the 'noob server' for awhile. (Still am, haven't gotten any better but none the less, great free game)
Then you can upgrade though getting kills to the next which is a bigger guy who is easier to hit but still can climb and stuff. He attacks by basically 'latching on' where the guy can't move if you get him and are repeatedly attack him, so if you're behind them unless they're good with moving the mouse a lot really fast (It puts resistance on your mouse so that if you try to move it automatically starts going towards where you where facing) they're usually pretty much dead then. You can also go them to the advanced, which allows you to spit an acid cloud in front of you which does damage over time. A lot of players use these guys, they'll hide behind something then when you come out of a door way or behind a corner they pop up, poison you, and run away. Then there's the marauder, he is like the basilisk except his power is that he can jump. He can jump off walls and stuff and build up a lot of speed, he's really hard to use but I'm sure you can but really good with him but I never did, I almost always play human when I can He can't go up walls though, I don't remember what his advanced ability is... Ah well. Next is the Dragoon. The Dragoon is much bigger and has a powerful pounce attack, he can also attack sorta like the basilisk but I don't think it locks your mouse, the advanced version lets you launch 3 dart sorta things and a lot of people will get these so they can snipe at the humans. (Not really snipe, the maps are pretty small, but we'll get more on that later.) Then you have the Tyrant, the Tyrant is a huge monster of an alien and has tons of health and a very powerful attack. He takes quite a few kills to get. He can charge in which unleashes a loud roar to pretty much alert any human players that there is now a tyrant and unless you're at the base you're usually pretty fucked unless you have a minigun, which can easily spray the crap out of a tyrant. Many a tyrant have died at my hands trying to sprint up and destroy the turrets but I've taken them down with my minigun in my suit of battle armor
Now for a bit more clarification on building and such. For the humans you can spawn as a soldier (The stuff I said you start with before) or you can spawn as builder which replaces your gun with a builder gun thingy. All stuff is built in real time during the battle. It's pretty much the same for Aliens except you can evolve into the alien if you want. Now, I said that the maps are pretty small but I haven't played this in awhile, there is 1 map that gets played mainly and its small, but there are other servers that have a few pretty large maps, so idk, go see for yourself. There are large maps as well. Think that sums it up, it's available on Windows, Linux, and Mac. (This is becoming almost a bunch of reviews from me of free games )
#5 Toribash - Toribash is a pretty amazing free turn-based fighter. I know that sounds like a huge turn off, but look at some gameplay. It's an amazing concept. There are 2 blocky guys facing at each other, each person controls 1. Each guy has points on his body that can be changed, his muscles. You change the muscles state, and that way you manipulate the body to attack the other player, once you figure out how the game works it can go 2 ways, 1 is a hilariously derpy and crazy game where you just kinda do random shit and play around, 2 is that you get good at the game and then you have a sorta tactical fighter where you actually compete and fight and stuff.
Now, the way this works is by 'frames'. You start off with a certain number of frames and then change your guys muscles and stuff and there will be an outline of what will happen when your guy does that (Without it you'd have no idea what the hell you're doing), then you press space (Or both of you if playing online like it should be played), and it plays out a certain set amount of frames, then you can change some more depending on what the opponent did etc., another 10-50-whatever frames and it goes like that until there are no frames and the person who did the most damage wins. There are also a ton of mods and stuff that change the shapes of characters, give them swords, make tetris shapes rain from the sky, ya know. What you'd expect. Still trying to figure out how to fight in the worm one.... Windows and Mac are supported, weird thing is that Linux used to be... I guess it's outdated or they stopped working on it, idk. I have the Linux version still, but there are no online games, even when I first got it and it was for Linux, but it seems that there are still people on Windows and stuff I think so try it out.
#6 - Dosbox games - Gotta mention these, I had fun with the alien based game 'Alien Trilogy' that is a doom kinda FPS, or Arena and Daggerfall, Oregon Trail, Warcraft 2 etc. Windows Mac and Linux. It takes a bit to figure out how exactly to install them, but it isn't that hard, but maybe I'm just a natural
#7 - Smokin' Guns - A very fun older counter-strike-esque game that's set in the Wild West. It's based on one of the Quake engines I think and basically you deathmatch in the Wild West, there are multiple modes where you have to rob a bank or deathmatches or duels and things. Mostly people just play deathmatch and Rob the bank. There's a good few maps, including one that's on a train that's really cool. Basically you start off with a trusty Remington Revolver and when you get kills you get cash, like Counter-Strike (I think ), and then you can buy stuff. You can buy new pistols, rifles, shotguns, dynamite, molotovs, a gatling gun turret, metal underarmor for your torso, a pretty good amount of variety. Now you can duel wield pistols, which is awesome. You reload each at once and some guns you must reload one bullet at a time, like the best pistol, Peacemaker I think. It's a very fun deathmatch kinda game that really needs more players. There aren't many players on but seems like at certain times there are. Just look at each server's info and if you see any guys with a ping limit then thats someone. Some of the servers try to trick you by putting wierd names for the bots... Awesomepossum... I'm looking at you, AI So yeah, if that interests you at all try it out. It's a very fun free game. Definately gives the feeling of a western badass when you burst out of a saloon dual wielding peacemakers and dueling some guy while probably being shot at by some guy on the sidelines Windows, Linux, and Mac!
#8 - Cuboid Sandbox - This is a little game/simulator that was made for the Ludum Dare Contest, it's a fun little game where there are 3 different colored factions, Blue Red and Yellow, you can plop down 1 of them and after a bit it'll sorta halve itself to make a baby. They'll die pretty quickly if you don't give them food, so you plop down an appropriately colored food. The best part really is just turning on random spawning food and them watching the chaos as the 3 colors get bigger and die from moving to new foods and get in fights with the others as they branch out and one of them usually gets lucky and owns all the others. Pretty fun little game thingy to mess about with if you're bored. Windows, Linux, and Mac as well as playing in browser! Though you need Unity to play in browser so download it if on Linux.
#9 - Air Buccaneers Beta - Haven't played it yet, but it looks fun and I think it'll be free-to-play in the future. You go around on airships and repair your ship and shoot cannons and fire out air mines. Kinda hard to explain, check it out. Similiar to Guns of Icarus.
#10 - Hedgewars - Ever wanted to check out sorta what worms games are like but didn't want to pay for one cause of all the other amazing cheap games out there like FTL? #Randompromotion Do not despair. Check out Hedgewars which is a sorta free version of Worms where you are little pink hedgehog thingies... Yeah. Pretty fun, there are people in the servers usually when I check so check it out. Windows, Linux, aaaaaaand Mac.
And that's all for now! Maybe I'll update it or make another one of some more, cause believe me, I got more I'll make a part 2 sometime, gotta go into the depths of my installed programs or even currently uninstalled ones etc. etc. so I can wrap it up.
Maybe I'll play Battle for Wesnoth as well so I can figure out what the hype is all about and see if it's worth mentioning officially
