I’ve recently begun to use OpenShot on Ubuntu Linux to edit a series of short screencasts with, and holy smoke what a pleasant surprise. Stable, easy to use (including a polished and smoothly responsive UI), a nice selection of effects and transitions, and pretty darn stable to boot:
It’s pretty much based on the iMovie paradigm, before Apple screwed too badly with it. Lots of advanced goodies which the competition doesn’t have, like fancy 3D animated and SVG titles via integration with Blender and Inkscape. Built-in support for insta-upload to YouTube. Even the documentation is great. Between Ubuntu, ffmpeg, and OpenShot (oh, and Audacity for the audio), it’s entirely possible to put together high-quality screencasts for zero software cost.
OpenShot is totally worthy of a donation, which I have happily made.