An integrated development environment for AS/400s originally introduced in 1988 by Synon, Inc., Larkspur, CA (derived from and pronounced "sign on"). As the dominant tool for the AS/400 platform, it provided an upper and lower CASE environment that generated COBOL and RPG code. Founded in England in 1983 by Simon Williams, Synon also built the Obsydian product, an object-oriented PC-based environment that is used to develop C++ code for Windows clients and RPG code for AS/400 servers.

In 1998, Synon was acquired by Sterling Software, in turn purchased by Computer Associates in 2000. The Synon products were first re-branded as CA's COOL:2E and COOL:Plex technologies and later Advantage 2E for iSeries 400. In 2004, they became AllFusion 2E and AllFusion Plex.