Didn't AOL for DOS run GEOS? I wondered why my 386SX-16MHz could run AOL's windowed and mouse driven GUI so fast but crawled with Microsoft Windows 3.1
They stopped using it when they stopped supporting DOS and switched to a Windows client. Older AOL for DOS 3.5" floppies can take the Geoworks files out and run them by themselves without the AOL client.
Geoworks kind of fell to the side of the road, but it still exists in some form at Breadbox.com: http://www.breadbox.com/
Like GEM, OS/2, Vision, Desqview, Geoworks kind of got killed by Microsoft bundling DOS and Windows to make their monopoly. By the time Windows NT and Windows 95 made it to the market, people went crazy over Windows and forgot the alternatives to it.