How can I get OS X El Capitan and watchOS and iOS 9 without being a developer?
You can sign up for the public beta (available in July) of iOS 9 and OSX El Capitan at:

Apple Public Beta Signup

In the past, the Public Beta has delays release of a specific build a bit behind the developer betas so those builds won't be as potentially buggy or as up to date.

The new unified developer account costs $99 yearly. Sign up through the Apple Developer Site to get immediate access to watchOS, iOS 9 and El Capitan on June 8 and later.


The initial El Capitan download is 6.06 GB and downloads as a redemption code from the Mac App Store.
The initial Xcode 7 beta build is 4.22 GB and downloads from an ADC Downloads web site 


The big news with Xcode 7 is that it removed the requirement you be a paid developer to run your own code on your own devices. This will be huge for students of all ages with limited budgets.


  Xcode 7 and Swift now make it easier for everyone to build apps and run them directly on their Apple devices. Simply sign in with your Apple ID, and turn your idea into an app that you can touch on your iPad, iPhone, or Apple Watch. Download Xcode 7 beta and try it yourself today. Program membership is not required.


This new Xcode is available freely to anyone today to start coding and running apps even if your Mac and iOS devices are not yet up to the announced OS. You get more tools if you join the paid program, but the basics are widely available today.