Quaderno is a MIDI sequencer with some unique views, editors and controls. It has a combination of windows and functionality found in many other sequencers as well as a set of original ones that provide unique and useful ways of working with MIDI compositions. It can open and save standard MIDI files as well as a whole slew of proprietary formats for just about every editable element of a Quaderno sequence.
Quaderno's unique features and interface can be fairly difficult to figure out, especially if you are new to concepts of MIDI sequencing. The lack of on-line help makes learning the program even more difficult, but KO Studio's does provide examples and a tutorial which are available from the Product Download Page.