The Howling Oak is the racial capital of the Gilnean-Worgen. Gifted to the Worgen by Tyrande Whisperwind and the Night Elves, it serves as home to the worgen until they're possibly able to reclaim their city of Gilneas. It appears to be very similar to Tal'doren (" The Wild Home") in the Blackwald Forest. After the Worgen Questline is completed, King Genn Greymane appears inside the tree for a very short period and then he traverses to Stormwind City to council with King Varian Wrynn.
In the mean time, Gwen Armstead seems to be keeping everything managed until Genn's possible return. Inside the tree, you can find all class trainers and outside of the tree, you can find Mountain Horses: The Worgen Racial mount.