It definitely is an aftermarket system, since the -200s lack a factory FMS and of course also a GPS receiver... True, GLS works with two on the 737, but the older 777s were delivered with three so that each MMR gets its own GPS input for a GLS approach.
€: Duh, I should read that article first, its this thing:
http://www.universalavionics.com/products/uns1fw.aspx