Johann Baptist Peyer (1680 - 1733) was an Austrian organist and composer. The main source of his compositions is manuscript Mus. Ms. 1220, held by the Staatsbibliothek zu Berlin.
The music in fascicles 2 and 3 is more modern, more like the galant style, than you would expect for someone born in 1680. Some scholars therefore believe that the ascription to Peyer in this manuscript is an error, and that it is more likely that Andreas Bayer (who was born 30 years later than Peyer) is in fact the composer of this music.
Be that as it may, Bayer or Peyer, it is attractive music to play and to listen to.
The RW numbers are attributed to F.W. Riedel who published some research done on the manuscript this music is taken from. He probably created a catalogue for Peyer's music as well. Hence the abbreviation, for Riedel Verzeichnis (= catalogue in German).
(Notes with thanks to Auke at http:\\partitura.org)