One more addition from the open source community that is released under a GNU public license Cinelerra offers some advanced functions such as video composting that allows the insertion/conversion of keying and matte textures.
Its support for high fidelity video and audio at 64bits is acceptable as medium quality compared to high definition standards. It can work in both YUVA and RGBA color spaces making it a powerful video editing tool indeed.
The interface is comparable with most other software offering timeline, a viewer windows where you can preview clips and a compositor where you cut and paste video clips to make your video. New stable versions are released at a semi-annual basis which makes it one of the most current open sourced video editing software around. It however only runs on Unix-like languages including Linux and the likes.