Rogue Legacy, a rogue-lite from Cellar Door Games, that originally released in 2013 has now had the source code released. The game has Native Linux support and is rated Steam Deck Verified.
In the announcement on Twitter / X the developer noted they've been working with game porter and FNA developer, Ethan Lee, to make this happen who will be maintaining it going forward.
The game is not open source though, to be completely clear on that. It's source available under a custom license with certain restrictions, much the same as VVVVVV and is actually based on the license that Terry Cavanagh used for it. This is also only the source code, it does not include the assets - so you still need to own a copy of the game.
In their own announcement, Ethan Lee posted on Twitter / X that they intend to take on community contributions to it, and they're in progress on upgrading it to use SDL 3 that's currently in Beta.
Really great to see more developers open up the code for their older games. This way they can practically live on forever. It would have been even better if it was fully open source, but having it open like this is still a great resource for developer curious on what goes on behind the scenes to learn from as well.