Hi Richard,
Thanks for getting in touch! Right now, we do not offer a special license for WordPress multisite networks. We do, however, offer three tiers of licenses (Personal, Business and Agency) that will allow you to pick up the number of licenses you would need for the sites you’re planning to use with the calendar. We also have more information on WordPress multisite network licensing, if that’s what you’re looking for.
Please let me know if you have any other questions here on licensing and I’d be happy to help. 🙂
Cheers!
Geoff