Hey there,
I've been working on a emulator/sandbox for a while, and here is the current state: https://github.com/marijnz/BunnyEmu.
The main goal of it is to support all major WoW patches, now currently focussing on 5.3.0. The authentication works on all major versions, such does the world login on 5.3.0, but other than that, it's pretty much it. I know compared to other emulators, it's not really much. Although writing this from scratch without much knowledge from the subject took quite a while.
Now someone else has been helping me out recently, but to make some real progress, we could really use more people to help on it. Java is a relatively simple language and the whole design of the emulator is pretty straight-forward (but can still be a little overwhelming). It's always possible to fork and PR any changes. Lots of things to implement!
Also feedback or criticism is welcome, the "emulator" is by no means perfect and could use the opinion of other people than me! It's something new
Note that the code is based off i.a, Arctium, MaNGOS and JMaNGOS.