Install the CatBase server on your server and connect any number of users.
The basic licence includes two user licences; you can add as many additional users as you need.
The users can be on any combination of Windows and Macintosh computers.
The licences are concurrent, meaning that you can install the Client app on any number of users' computers, but the number that can connect to the server at the same time is governed by the number of user licences you've purchased.