I bought my very first Band in a Box program from a local music store going out of business.
I had never even heard of it, but the description on the outside of the package made me curious. Since then I have bought every update they have offered. To begin with all instruments were generated in MIDI. These days with introduction of Real Instruments, I finally get to play with real players and even know the name of “my” bassist and drummer. They never require any pay, do not need breaks etc. and put up with all kinds of alterations in tempo, chord changes and styles I like to make.
The input part consists of two parts; a "spread sheet" for entering the chords, the number of choruses tempo, key etc. The second part allows one to enter two melodic lines e.g. melody and background. Both melody and background (or Soloist, as it is called) can be both mannually or automatically harmonized. The program also allows for the chords to be outputted to external modules, e.g. the TC Helicon Voice Works, so that I can sing four part harmony, all by myself.
I take pride in writing all arrangements myself in order to avoid sounding like any other One-Man-Band.