Open Broadcaster Software is free and open source program for recording and live streaming. OBS is currently available for Windows Vista, Windows 7, and Windows 8 with Mac and Linux versions planned in the future. Both 32 and 64 bit versions are available and it's absolutely free.
Open Broadcaster Software has an API allowing developers to create their own unique plugins, giving them and others complete control of their streaming experience.
Also, the source code is available for all to use and change under the GNU General Public License v2.