Johann Gottfried Walther is among organists a well-known composer, thanks to his extensive oeuvre for organ: concerti, preludes, fugues and many choral preludes & variations. Many nice recordings of his works can be found on Contrebombarde.
These two variations on 'Von Gott will ich nicht lassen' are simple, playable on one manual, and quite effective.
Played on the Coci-Fritzsche-Dropa-Klapmeyer-Ahrend organ :)