The number of users in Synergy is effectively unlimited other than by your infrastructure and resources, so you can create as many as you want even on a single laptop computer. This is perfect for when you have various people using the system on one computer and want to know who did what – job sharing, part time workers, and temp workers are all examples of a situation where this would be beneficial.
However, the number of machines that can use Synergy at the same time depends upon the number that are licensed and the database back end being used. As a general rule, although the standard database can be run with multiple users it will be at the mercy of your operating system and its file and record locking limitations. If you will have multiple users connecting to and wanting to use the data at exactly the same time then a SQL Server database will give better performance. For anything more than two or three users a SQL Server database is pretty much essential.