IFTTT (if this then that) is cool glue for a whole range of mashups between different web services & social media. It lets you create 'recipres' that watch for actions then trigger events. No code required! For example: Add an note in Evernote when you are mentioned on Twitter.
The possibilities are quite endless and to help you get the creative juices flowing IFTTT has a pile of samples.
Today's announcement that IFTTT now supports GitHub brought a collective "cool" from devleopers universally.