There are many web based screen capture applications out there eg. Screentoaster. Screenr is another web application that lets you create screencasts without installing any software.

To begin, you just click the record button and your screen activity is recorded along with narration from your microphone. You can record any size you want up to 2560×1600 on a PC and 1920×1200 on a Mac.

The recorded screencast videos will be published high-definition flash format. Screenr allows you to share your videos via social networking sites like Twitter, YouTube or anywhere else on the web.