SeriousSamClassic is open source game engine version developed by Croteam for Serious Sam Classic, but it should work on (or be easily portable to) any system that supports OpenGL 1.3 and SDL2.

Note that while the Serious-Engine source code has been released under GPL, you still need to legally own the game and provide Serious Sam Classic The First Encounter and Serious Sam Classic The Second Encounter the game data to play. See the How to Install section for more information.