This site tries to gather open-source or source-available remakes of great old games in one place. If you think that something is missing from the list - please go to our GitHub repository and create an issue or even a pull request!
Since all these projects are open-source you can help them and make this world a better place. Or at least you can play something to appreciate the effort people put in them.
Similar resources:
Free Gamer, a blog dedicated to open source game news
Unix ASCII games, a list of opensource text-based games
List of Open Source Games, list of open source games in mature/beta state
Awesome Open Source Games, list of open source games and game-related projects that can be found on GitHub
LibreGameWiki, the free gaming encyclopedia
A is a game where the executable and sometimes the assets as well are remade open source. Some of these games aren't exact remakes but evolution of original ones, which were eventually open sourced.
A is a game which is very similar to or heavily inspired by a game or series.
An project is the official source code release for a game that was formerly closed-source, maintained by the original creators and has minimal changes.
A game is one which has similar gameplay but is not a clone.
A is not a game, but something that assists in playing or modding the game, such as a high resolution patch, or resource extractor.