Sometimes it is useful to work with a team to collaboratively solve a problem, such as breaking one down into two parts and solving them individually, or just sharing code with each other quickly. Here is a list of online compilers that support this feature.
Repl.it - has a clean interface, supports more than 50 languages, can download code, supports reading from a file, supports auto-completion, has multiplayer mode for up to 50 people, and supports live changes in the code but has only public repls for free
JDoodle (C++ / Java) - supports 72 languages, can download code, supports pre-written stdin inputs, has interactive mode (Google Code Jam), supports collaborative mode, and contains a chat, but contains ads and does not support live changes in the code (you can copy and paste to the chat though, but cumbersome)
This is for those who are too lazy to log in to Repl.it or just want to share something quickly.