_why enables you to run ruby (irb in particular) from a web browser, and github allows you to edit code that's under version control from a web browser.
Is there anything that allows you to do both, ie edit code and run it, from a web browser?
What is wrong with editing locally, commiting, and having a git hook that pushes the latest version to the correct location?
http://www.kernel.org/pub/software/scm/git/docs/githooks.html