Puffff, tons of not implemented features, but Mangos community do what they can. 4 Example:
Vehicle System. (RSA implementation is good enought ;-) and works with multimounts)
+ Sota Battleground (You can find some versions on ankso, kero99, bwsr... repos)
+ IC Battleground
+ Wintergrasp
+ Random Battlegrounds (You can find a path in insider42, rsa, kero99... repos)
+ Dalaran Arena (same as random)
+ Orgrimmar Arena " " "
Dungeon and raid finder. (Cyberium is working on the first one with some help of SPP_ and some other people)
MMAPS. (faramir118 is working on)
VMAPS for Gameobjects (Especially 4 Collision spells). (Silverice is working on)
Multithreading (Mtmaps?? But is not the best way)
Calendar Events
Some class spells and talents
Cross Realm Battlegrounds and arenas (Nezhul developed a Cluster for this, but i don't know if it works)
Instance Cluster realm for Dungeon / raid finder with cross realm groups.
GM surveys? Ticket assignment?
NPCs on transports
RAF (Recluit a friend ingame features)
Server Side change faction / race
...
Performance progress:
Visibilty and reloc by silverice (Now with help of Ambal)
reactor pattern (faramir118 is working on with Ambal's help)
Prepared Statements (Ambal is working on)
World_task (May help in mtmaps enviroments) (Ambal is working on)
...
Probably tons of more features... but now MaNGOS community is more active than some time ago ;-)
And of course... i hope in the future MaNGOS will support Cataclysm ;-)