Invision - Prototyping and collaboration for design teams
ProjectHuddle - Get design feedback and client approval using WordPress.
Dotarchy - Pick a topic, discuss it, make some Friends
Savahapp - The all-in-one design sharing, collaboration, workflow and app prototyping platform
Start on Android by Google - Developer program to optimize your app before you launch
Specfox - A free platform for creating beautiful website and mobile app specification documents for your team. No more word templates!