Quarterdeck Extended(?) Memory Manager. A once popular DOS memory manager ("memory managers" allowed programs running in 16-bit DOS to use a flat 32-bit address space). At those times, it was essential to have one to provide EMS (also provided by MS-DOS' EMM386.EXE) and XMS (provided by HIMEM.SYS in MS-DOS) memory for your favorite games. At the days of the 640K barrier, QEMM managed to optimize your conventional memory much better than MS-DOS' memmaker did, many times reaching 640K free even with such luxuries as loaded CD-ROM drivers! Later on, as Windows 95 got spread and standartized, those were no longer necessary.
(IBM's PC-DOS provided a memory optimizer of their own, called Ramboost from Central Point Software in the latest releases.)