Take a look at Harmony 2007 (www.domialifestyle.com) - it's a home automation platform, with support for several hardware options (X10, BBS, CBus, Dupline, Rako etc).
Harmony 2007 is a complete rewrite of the former Harmony 5.x range - written in VB.Net and C#
It comes with a DotNet API that enables full control over the "core" messaging system.
There's an active community on the forum (see support section of domialifestyle).
*disclosure* I wrote most of the components, and I'm now the manager of the Harmony / Domialifestyle Business).
Hope this is of interest,
P.S. feel free to contact me directly if you feel it's appropriate.