This site hasn't been updated in five years, but it's still an impressive list (assuming the links still work):
http://freeware.remakes.org/index.php

There were several games that got the same treatment. Doom, Castlevania, Diablo, even a Megaman one i couldn't get to work.

Although they greatly change the mechanics while still feeling very similar to their source material.
Interesting. Reminds me of a site that archives some older games and makes them easy to start up and play. Doesn't take long to remember and realize why they aren't played much currently, namely because we're missing manuals and the like.

Here another free games

Paranoia

Paranoia 2 Savior

Blob Wars Metal Blob Solid
A solid 2D platformer. You got guns, grenade, and lot's of enemies to kill. Awesome. Beat it some years ago.

Blob Wars 2 Blob and Conquer
Sequel to Blob Wars. This time it's a 3d platformer/shooter. Haven't finished yet. But you get a sidekick this time

Interesting thread, herecomethe2000! +1
Let me add two play-worthy titles to the list (non of them open-source, but available for free from the publisher's site):

- [[url=http://www.screen7.co.uk/games/download/Downfall1.4_Free_Setup.exe]direct link] (the original from 2009; it's also included in GOG's version of Downfall: Redux)

- Heroine's Quest: The Herald of Ragnarok [direct link]

Both available at Screen 7.

Now that we have another thread like this with an OP who'll presumably keep the list updated, shouldn't it pick up from where that previous one which was linked to earlier left off? OP there not updated since 2013, so plenty posted since not covered in one place, and those who posted them may want to move their posts here if they're still relevant.

I don't know how I forgot to mention:
NetHack.
Great game.
100% free.

As always IJI

GO PLAY IJI.

RIGHT. NOW.

No, I will have to check it. Did it change my hated feature from RCT2 that you can either get money from entrance fee OR from the rides? i.e. if you can change the price of one of them the other is set to free and you can't do anything about it - it almost ruined my whole experience with RCT2

Yep, you can set it so that you can set both. That was something that massively annoyed me as well. I used to simply skip those levels where I could only charge an entrance fee. And you know what else? You can set it so that construction is allowed in pause mode!

Cool, thanks a lot for that! I'll download it and play it then :)

Sure thing :) Enjoy!

The best I had so far: Path of Exile
If you know Diablo series that popularized the arpg genre, well, Path of Exile is currently the best arpg out there, besting even D2 and D3. imo.

Later Edit:

Folks, remember to write a few words about *why* said game is worth recommending. Just a single line describing the game makes a world of difference! :)

Can the games listed be free to play or can they only be 'full free games' with no IAP?

Hard to find good co-op players for that one though, and the single player mode isn't that much fun.