Knismogenic

We use MIDAS in our school (although we use it primarily for external lettings, as we use SIMS for lesson timetabling) and have been really happy with it and their support has been very efficient too! Their self-hosted option allows single sign on through ldap authentication, and there is an API available to (although I haven't personally used the API, as it seems to be available as an optional addon rather than included as standard)