This is the main "brain" of the system. It hosts a number of functions and at least one instance is always required per library. It acts as an FTP server for the security cameras, broadcasting server for the speaker system and an IO controller for the building automation and electrical door lock controls.

The SOL controller is a single Windows service. Settings are controlled mostly through Management utility, as with any Supa software. The actual configuration of the self operated library is done using a separate tool, SOL admin.

It is possible to have more than one SOL controllers running in a library. Typically this would be in a larger library, where different parts of the library need to have different schedules and possibly have different entrances to control. Each SOL controller can control one IO module, which has a fixed number of input and output channels available for control and monitoring. Extending beyong this limit means adding more SOL controllers.