Want to revisit the classic GTA III and Vice City? You should take a look at re3 and reVC which not only provide the source code, they also upgrade the experience for both. Available on GitHub in a combine repository split across different branches for GTA III and Vice City, it has been tested by the team working across different systems including Linux.
Just like other game engine reimplementations, they do require the original data files so it needs a small amount of work to get each going. Considering the age of both though, the re3 and reVC projects are now probably the best way to play each of them on a PC.
Originally started in 2018, it seems the COVID-19 pandemic gave them a bunch of time to get it finished and out the door. They also mentioned their intention to work on the Liberty City Stories game which they've started in a reLCS project.
Amazing work from a dedicating community, which should enable these games to continue living on. They sit in a legal grey area though depending on what country you're in, as this type of reverse engineering is usually frowned upon, especially by the rights holders like Rockstar. The actual project has no license attached to it.
Check it out on GitHub.