AppToService is software that makes any Windows application a service.
Any application which needs to be "always on" - whether a user is logged in to the computer or not - can benefit from AppToService.
What AppToService does is, simply, turn any Windows application into a Windows service.
This has several implications. The app can then run when no user is logged on. It can run as a user other than the logged-in user. It can start when Windows starts.
The usefulness of this is mostly for applications which need to be always on - a database, a mail server, or a security tool, for example.
AppToService also can be used to allow a program which needs one particular user's privileges to be running no matter who is logged in.