The Offhandopera (!OHO!) is an impromptu opera. There is a libretto and a working method (rehearsals, conducting). The participants create the music, the singing, the speaking; there are overtures, interludes, arias and choral passages. It is also an opera that translates content (the libretto text) into music, but each performance is unique and unrepeatable. The stage design and theatricality are rudimentary and the performance is rather concert-like.
The performers create the opera as an ensemble, so each performance is a creative social example that utilises collective creation to produce a work of art.
Reinhard Gagel has performed numerous offhand operas at exploratorium berlin from 2012 to 2019; he is now starting a new series.
Further information about the concert can be found here: https://exploratorium-berlin.de/events/buehne/oho-offhandopera/