As promised, Apple released a public beta of OS X Yosemite on Thursday. The beta gives Mac users the opportunity to participate in the testing process, and get a taste of what's in store, before the new operating system officially ships this fall.
Getting early access to OS X Yosemite will be great, but don't forget it's beta software. Things will be broken and features will be missing. Don't expect it to perform like a final shipping product.