I've been very excited about Roslyn since I heard Anders Hejlsberg speak about it at Microsoft's Build conference, but I never had a use case for it besides the tutorials and samples included with the CTP. One of the cool things that came with the CTP was the new C# Interactive window (a REPL environment) it added to Visual Studio. With it, I can execute C# against my solution on the fly. This is extremely useful for doing things like testing regexes, comparing the results of different method overloads, or quickly testing a method I just wrote, without requiring me to rebuild the entire project or solution.
The idea behind Compilify is to bring that same interactive environment to the web.
The idea behind Compilify is to bring that same interactive environment to the web.