EtherPad : Etherpad is an Open Source online editor providing collaborative editing in really real-time powered by Node.js
RegExr : RegExr is an online tool to learn, build, & test Regular Expressions (RegEx / RegExp).
metaflop : Metaflop is an easy to use web application for modulating your own fonts. Metaflop uses Metafont, which allows you to easily customize a font within t...
SQL Fiddle : A tool for easy online testing and sharing of database problems and their solutions.
Ready for Rails 4? : Check easily whether a gem is ready for Rails 4 or not.