Developers of the Smart Architect range of architectural extensions to AutoCAD and AutoCAD LT, as well as a 3D modeller, and a LISP enabler for AutoCAD LT. http://www.drcauto.com/
The Trace Elec Pro electrical schematic solution for AutoCAD, and the Trace Plant Designer package for industrial installation and piping design. http://www.traceindustry.com/