- Mac OSX is built on top of BSD-UNIX which is open-source.
- Odeo.com used code from iPodder which is an open-source project for their OdeoSyncr component.
- And recently, Joel Spolsky announced CoPilot which also uses some open-source VNC software.
See a trend?
Also read, Rashmi Sinha's article where her main emphasis is on identifying open-source products that can be sold if they have better usability.