We are using Maestro Performer by BocaVox, LLC. We have used it since 2009 and I am extremely satisfied with it! I would definitely recommend Maestro. Here are some of the reasons why:
1) Almost 100% uptime
2) Fantastic service after sale
3) Ability to customize their product to the need of our statewide virtual school
4) Ability to build successful integrations
5) Problem-solving: If you bring a business process to them with which you are struggling, they will do their best to provide possible solutions to you.
6) Ability to update and upgrade: They can run simple new releases almost seamlessly with a minimum of downtime. For major product upgrades, they will work with you to schedule a time that works best for your school.