Db Maint - Single server edition
One license allow the Db Maint server to be installed on one server. Any number of clients can be installed.

Db Maint - Multiple server edition
One license allow the server to be installed on five servers. Any number of clients can be installed. You can log performance conters from a total of 25 servers on one license.

Db Maint for MSDE
The same feature set as the regular Db Maint but will only work against MSDE. This has a substantially lower price than the regular Db Maint.