If you love being on the bleeding edge of technology, and don’t mind risking your machines stability, you can register for Apple’s Beta Seed program. Previously Apple used to restrict access to its Beta software to only registered Apple Developers. (Costing £99 a year)
However, they recently changed tac and they are now inviting all users in. You can register using the link below:
OS X Beta Seed Program – AppleSeed
It’s worth noting that these beta’s shouldn’t (really) be installed on your production machines, and you should ensure you have a backup prior to installing.