ExecuCalc, from Parallax Systems, Inc.: Released in late 1982, ExecuCalc was the first mainframe "visi-clone" which duplicated the features of VisiCalc on IBM mainframes with 3270 display terminals. Rex Swain designed and programmed the product using IBM's VS APL, GDDM, and AP124X for mainframes running VM/CMS and MVS/TSO.