Members of the Apple Beta Software Program are now able get their hands on the first public beta version of OS X El Capitan. This follows the recent release of the third OS X El Capitan developer beta.
This is not the first major version of OS X to get the public beta treatment. Prior to its retail release last year, OS X Yosemite received a number of public beta releases, which continued even after the system hit the Mac App Store last fall.
Please keep in mind that while Apple is opening up the latest version of OS X to more people, this is still beta software. As such, it's likely that you will encounter at least a few issues, so install it at your own risk.