Apple has released public beta tests of individual Mac apps in recent years, but OS X itself has largely been off-limits unless you've registered as a developer. That changes now that Apple has launched the OS X Beta Seed Program. Starting with OS X 10.9.3, you can try pre-release operating system updates by signing in with a garden variety Apple ID; oddly enough, you still have to sign a developer-style agreement promising to keep some details a secret. We wouldn't sign up solely because of the upcoming Mavericks update, but the program represents an all-too-rare opportunity to both preview features and provide direct feedback as an everyday user. If you're willing to live with a few bugs, you can start with your first beta at the source link.
Apple OS X Mavericks