We integrated MESS core into MAME Plus in the hope that MESS would get wider attention that it deserves.

"console games tend to push things harder than arcade ones, and often abuse chips in ways the arcade games don't", so that console emulation may potentially improve the level of accuracy in MAME. currently we have 3 drivers (ie. NES, SNES, Genesis) enabled, to evaluate console emulation in the MAME framework. we prefer not to have a fixed game list, as the MESS window UI already gives a console-ish emulator look and feel.

http://www5.emu-zone.org/host/mameplus/