Well.. implementation started in C++ (for both client and server)
1) For now, we are using SDL to make a simple 2d client (just for testing.. we will probably switch to OpenGL).
2) For the networking part, we found this: http://vichargrave.com/multithreaded-work-queue-based-server-2/
it's a nice set of objects/methods for producer-consumer model, queue based (they implement mutex inside, so they are really handy).
3) For client/server message protocol, we wanted to use JSON "format".
When we'll finish networking.. the rest it's a matter of design
[EDIT]
Ohh.. and we need to choose an efficient db ...
[EDIT]
Just started studying noSQL databases, in particular MongoDB ... this should be a good compromise between perfomance and convenience.