CodeShare, a small but very useful tool by Lee Munroe, is something every developer may have use for. CodeShare allows you to share and edit code in real time with whoever you like. You simply share the unique link with anyone and they can see you typing out code in real time. They can even join in on the coding and start typing out their own code.
I could see this becoming very handy if you're working with another developer. Hook up a Skype call and start coding together, working out solutions and fixing bugs.