Technically, there is no table that has that information, but DB2 V9.5 has some administrative views that will supply the information. Check out this view:
If you don't have version 9.5 you can use the following table function:
Go to the DB2 Info Center for your release and search on one of the above options to get more information on how they work.
If you have V9.5 the above view is preferred and I think the table functions will eventually be phased out.
I doin't think there is one for "list active databases" because the above view or function assumes you are connected to a database already (but not 100% certain about that).
M. A. Feldman
IBM Certified DBA on DB2 for Linux, UNIX, and Windows
IBM Certified DBA on DB2 for z/OS and OS/390