Firebird Question:

Currently there is no easy way of doing it. You can bring database to some of shutdown modes, but it affects all users. If you use Classic you can (with some effort) find the users process by detecting the IP address and open database files of that process and simply kill that process. With Super Server it is not possible as the connection is run in a thread of multithreaded SuperServer process.

There are plans for future versions of Firebird to address this. For example, version 2.1 introduces ability to cancel running queries (by deleting the relevant records from MON$STATEMENTS table).