Uniface
Uniface is a multi-platform RAD client/server toolkit that was originally released for DOS in 1987 by a Dutch company of the same name but gained a client version for Microsoft Windows a few years later, server versions for sundry UNIX and Unix like systems in the early 90's and a Client/Server version for 32 bit OS/2 in 1993. Primarily popular in Europe for a while Uniface on OS/2 had extensive support and it may have been the most popular Client/Server of any sort on the system, France Telecom had no less than 10 thousand seats OS/2 seats using it in 1993.