Today I noticed a new site from Esri, and it's called 'ArcGIS for Developers'. This website consolidates the web, mobile, and introduces some new desktop APIs.
The one that really excites me is the Qt API because I'm a fan of C++. I also introduces the new approach to open for Esri by using GitHub for code sharing. I've only started playing, but I'm excited to see what comes.
Check it out here: http://developers.arcgis.com/en/