Steve and I are working on a MP version where its like you summon the creeps to attack the other place, and you can still build a tower...much like the VS TD on WC3FT.
so far we got the chat working, servers working, and creep spawning half working..But other then that MP is going great.
EDIT:
Also check the website page alot, The blockland version of PTD (the one i posted) was only V2....The current is V3.5