As a gift to King Frederick the Great (Frederick II of Prussia) after his visit in 1747, J. S. Bach wrote a set of pieces based on the fugue subject that Frederick shared with Bach on his visit. The result was the famous collection of pieces known as the Musical Offering (Muikalisches Opfer, BWV 1079). The account of Bach's visit is a fascinating story, a recommended read for anyone not familiar with it.
The collection contains music for trio sonata, solo keyboard, and other small combinations of instruments, as well as contrapuntal pieces for unspecified instrumentation, as was the custom in those days, since music was meant to be versatile, and except in the most virtuosic situations, was transcribable between different instruments of the same range.
Video by Jos Leys (http://www.josleys.com) and Xantox ( http://strangepaths.com/en/ )
playing it on the harpsichord