SPOJ (Sphere Online Judge) is an online judge system with over 200,000 registered users and over 20,000 problems. Tasks are prepared by its community of problem setters or are taken from previous programming contests. SPOJ allows advanced users to organize contests under their own rules and also includes a forum where programmers can discuss how to solve a particular problem.
Apart from the English language, SPOJ also offers its content in Polish, Portuguese and Vietnamese languages. The solution to problems can be submitted in over 40 programming languages, including esoteric ones, via the Sphere Engine. It is run by the Polish company Sphere Research Labs.
The website is considered both an automated evaluator of user-submitted programs as well as an online learning platform to help people understand and solve computational tasks. It also allows students to compare paradigms and approaches with such a wide variety of languages.