If you're the type who loves beta testing software but didn't (or couldn't) jump through the hoops to be a part of Apple's developer program, fear not. The company has opened beta testing for OS X Mavericks to the public.
Apple puts it thusly:
The OS X Beta Seed Program gives users the opportunity to run pre-release software. Test-drive beta software and provide quality and usability feedback that will help make OS X even better.
You'll need to sign up for the beta program — and sign a confidentiality agreement. Apple will then send you a Beta Access Utility program, and you'll be good to go for pre-release versions through the Mac App Store.
Join now: Apple OS X Beta Seed Program