CTFd is described as 'Simple CTF engine written in python'. There are four alternatives to CTFd for Self-Hosted solutions, Docker, Linux and Ruby. The best alternative is Mellivora, which is both free and Open Source. Other great apps like CTFd are Hack the Arch (Free, Open Source), MITRE CTF Scoreboard (Free, Open Source) and BOCA Online Contest (Free, Open Source).
mellivora - Mellivora is a CTF engine written in PHP Features Arbitrary categories and challenges. Scoreboard with optional multiple team types. Manual or automatic free-text submission marking. Challenge hints. Team progress page.
Although each local site runs its competition independently (for example, the programming environment and the submission systems are controlled locally), the problem set and test cases are prepared by a unique committee