Cloud9: IDE in the cloud
Cloud9 is a cloud based IDE that works completely within the browser. It even provides a full linux terminal within the browser. It is ideal to try out some open source language/framework quickly without doing the full setup.
Currently it supports nodejs, PHP, python and ruby out of the box. There are plans to support .Net in the future. It allows one-click deployment to cloud platforms like Azure, CloudFoundry and Heroku. PFB screenshot of my attempt at a simple nodejs program :).