Codeforces

Codeforces (Russian: Кодфорсес, sometimes written as CF) is a website (founded 2009) that hosts competitive programming contests. It is maintained by a group of competitive programmers from ITMO University led by Mikhail Mirzayanov. Since 2013, Codeforces claims to surpass site TopCoder (founded 2001, which also has a significant competitive programming component) in terms of active contestants. Codeforces along with other similar websites are used by some sport programmers, like Gennady Korotkevich, Petr Mitrichev, Benjamin Qi and Makoto Soejima, and by other programmers interested in furthering their careers.