MTuner

If you work on game development tools (or are a student/enthusiast) you can get an invite by direct messaging your email address to @thetoolsmiths. If DMs aren’t open poke the account first and it will follow you.

If you have an email that is under the following domains: activision.com, treyarch.com, infinityward.com, bungie.com, ea.com, frostbite.com, unity3d.com, epicgames.com, retrostudios.com, blizzard.com

You can use the fast signup process by using this signup page and providing your email.