My main jazz band is an ensemble, 3 bassists, 2 drummers, 3 keyboard players, a couple of singers, 3 sax players, 2 guitar players and a few deps.
Everyone is allocated a number of gigs through a 3 month period, these are sent around on a programme, with the date, venue and crosses by the name of each musician to show what they're doing. This is updated as new gigs come in. It works well, and is quite simple to operate, even for such a large ensemble.