Turtlebot
A few things changed from groovy to hydro.
Major Changes
Gazebo
Finally, simulations for kobuki and turtlebot. Thanks to the gazebo team and Marcus for resolving all of the tweaks and fiddles to get gazebo re-integrated with ros and turtlebot after all the DARPA changes.
Rocon App Platform
The old unsupported app platform has made way for the rocon app platform. At the moment, you shouldn't notice too many differences to the way it allowed you to work with android. The only really notable difference is that it uses a private/public master pair so that robot-android app pairing is properly sandboxed. Many of the other changes are under the hood, with the hope of being able to enable multi-turtlebot easily in the near future. Tutorials start with the app manager.
Android
Part of the overhaul for the app platform was to straighten out the android development environment so that it is just a matter of opening android studio and clicking to start your android app for pairing with the turtlebot. To do this, we've made some sweeping changes to the development environment - google's new android studio and android gradle plugin, aar's, a ros maven repository and rosjava debs. You can get started browsing the rosjava and android pages, and then go to town on the android turtlebot app tutorials.
Catkin
Absolutely everything is now catkinized.
Minor Changes
Kobuki C++ vs Kobuki Ros
Kobuki driver code is now split between two stacks - kobuki_core and kobuki. This dumps the pure c++ code into one stack and ros code into another which makes it easier for various exotic compiles.
Kobuki PID Configuration
Kobuki has a new 'experimental' firmware release that supports configuration of the robot's internal PID settings.
3d Sensing
Not much different here except that it now uses the improved openni_launch arg configurations rather than hacking our own openni_launch equivalent.