Well, here goes my very first post here in Lainchan. Though I must add that I am a long time user of the site.
I am all in with free games. As in free beer (see mmos) and as freedom of speech. The games that will be listed are actively developed ones. The Score thingy will be very personal and it will be based in the comparition of the game with it's free alternatives, not with the paid ones!
Here goes a nice list with a few comments:
> Battle of Wesnoth https://www.wesnoth.org/ :
Even though it has already been posted, I'll add a description to it. Great strategy game. Whit a pretty big modding community. It is old style, I love that personally. It may not very deep regarding posibilites, yet it focuses a lot in the strategy. I haven't played it much due to time constrains (work and studies), yet I would totally recommend anyone to give it a go.
> Xonotic http://www.xonotic.org/ :
A personal favourite, I don't know how many hours I have spent on it, but man, is it good. Quake clone. Small yet loving community, though we may be a bit elitist we always welcome whoever wants to learn. The community eventhough small is very close, everyone knows everyone. Just get your reflexes checked, it is fast as... Quake. It is mostly a multiplayer experience.
> 0A.D. https://play0ad.com/ :
Oh... Another old beauty. It feels like the old Imperiums or Sparta. There is a lot to be done, but it is very nice indeed, specially if you want to remmember the good old days of RTS games. There is nothing much else to say, just give a nice try. However, I must warn you, the AI is... AI, it is going to give you a nice taste of it's capabilities, don't cry if you lose, you have been warned.
> Minetest http://www.minetest.net/ :
Best open source Minecraft clone, by a long shot. Nice community, modders are relatively active. But it is far from achieving what minecraft is. Minetest could be better described as an advance crafting game, it still needs quite a bit of development to replace minecraft.
> Flight Gear http://www.flightgear.org/ :
Another personal favourite. A flight simulator. But you can have as much fun as with a game. IT IS NOT A GAME. It is a simulator indeed, it even teaches you the terminology, procedures, laws, etc regarding fliying. It is a shame there are not a lot of people in the multiplayer where I usually fly.
> Freeciv http://www.freeciv.org/ :
Civilization inspired clone. It tries to copy the feeling of civilization, the old ones, not the new versions. Has multiplayer. I haven't played it enough to give it a score, but the launcher could be greatly improved.
> MegaGlest https://megaglest.org/ :
Could look worse. Could be less fun too... Semi-fantasy RTS game. A must try in my opinion, but it needs some improvements over all, not in the graphics though.
> Unknown Horizonts http://www.unknown-horizons.org/ :
Remmember Patrician? I haven't played this game, but I have heard very good things about it. I'll give it a try and so should you. It is a strategy/building/trading game in the old style.