Hi - re: unrealBook - someone mentioned using it to change keys, tempos, rhythm ... I think that must be some other app. unrealBook is a music display program; it displays PDF files. It has lots of great features for Set Lists, searches, metadata (keywords), organizing PDF files ("sheet music") and such. It does not have any features related to key changes, rhythms, tempos. It can send MIDI commands though, so maybe your friend was using its MIDI abilities to change the key/tempo/rhythm of a piece of hardware (or software synth/sequencer?)

unrealBook itself has no "sequencer" or rhythm machines etc.

Jim