ELF is described as 'Extensive, Lightweight and Flexible platform for game research, in particular for real-time strategy (RTS) games. On the C++-side, ELF hosts multiple games in parallel with C++ threading'. There are three alternatives to ELF for Linux, Mac, Windows and Self-Hosted solutions. The best alternative is OpenAI Universe, which is both free and Open Source. Other great apps like ELF are SerpentAI (Free, Open Source) and OpenNERO (Free, Open Source).
Serpent.AI is a simple yet powerful, novel framework to assist developers in the creation of game agents. Turn ANY video game you own into a sandbox environment ripe for experimentation, all with familiar Python code.