Here's the Changelog :D
Update: Minecraft 1.9.2 is now available and fixed the issue that some players could not connect to some servers or their realms.
1.9.1 notes:
Woooosh. That’s the sound of the elytra and the main feature of the 1.9.1 release of Minecraft. The second notable change is a new property (toughness) for armor that “makes diamond armor useful again”.
Apart from these awesome additions, we also fixed some reported bugs and improved the performance and memory usage of servers a bit. Command blocks in custom maps should also behave much better now, especially with long sequences that are executed every tick.