Well that’s 2 tools instead of one, but they seem a bit overlapping and a bit complementary at the same time.
Ideone.com lets you submit small code snippets in order to test them (live compilation and run). They support about 60 languages (I didn’t count myself, but that seems quite accurate from their impressive list), from the classic C(++)/PHP/Java/Javascript/… to the more uncommon R/Octave/Scala/… and even quite a few I had never heard of before (bc/Unlambda/…)
Codeboard.io lets you work online on whole projects. They seem to be very recent (a project I created about a month about was ID 1500-ish while another project I created a few days ago was ID 4500-ish), and they only support 6 languages so far: C, C++, Eiffel, Haskell, Java, Python.
Nothing much to add… just give them a try whenever you need a quick way to test your code without setting up a whole development environment 😉
I like to use http://onlinegdb.com for my C/C++ programming online, as it has debugger and compiler both.