Inventra is the Intellectual Property (IP) arm of Mentor Graphics, the CAE company.

The M8051 appears to be a synthesizable 8051 core for ASICs or FPGAs.
http://www.mentor.com/inventra/...ontrollers

If you are interested in such things, you might also be interested in the Triscend E5 Configurable System-on-Chip (CSoC) family which includes an embedded 8051 microcontroller and programmable logic. The E5's microcontroller is actually a super-set of the 8051 that operates three times faster at the same clock frequency.
http://www.triscend.com/products/indexE5.html