RPG
From MidrangeWiki
RPG, which stands for Report Program Generator, is a easy to learn and understand programming language that is well suited for developping business applications.
There are X major versions of RPG currently in use... RPG II, RPG III, RPG 400, and RPG 4 (sometimes referred to as ILE RPG).
The midrange.com hosted RPG400-L mailing list is for discussion of RPG programming.