Vanilla world, Burning Crusade toolkit. Season of the Crusade bolts 2.4.3 systems onto Azeroth — and the counter reads 1 player online.
TL;DR
Season of the Crusade: 61 talent points at 60, BE/Draenei, jewelcrafting with sockets, arenas + honor system replacing ranking, new dungeon sets with TBC bonuses. Live site, 1 online. Listed tiny.
What it is
The interesting hybrid: not a progression realm, not pure Vanilla+. TBC classes, professions and PvP systems backported into the level-60 world. Launched last December per news archive (Molten Core Jan 20 posts).
Honest flag
One online at press time. Concept carries it, not population. Listed for the idea; watch whether TBC-systems-in-Vanilla finds its players.