Romcenter is a ROM manager, to manage collections of games supported by an emulator.

Its purpose is to give you the ability to:

View all games supported by an emulator plus all the games you have in your collection for it
Fix missing or bad-named games and ROMs in your collection (this will be analyzed later on), so they can be playable by the emulator

There are two main concepts in ROMcenter, “database” or “datafile” and “ROM path.”

A Romcenter “database” is where ROMcenter stores info about all games and ROMs supported by a specific version of an emulator. Such info can be either found in a data file or retrieved directly from an emulator (if it supports it).
MAME is an example of an emulator that when executed with a specific parameter, it displays all the games it supports and their contained ROMs. ROMcenter can automatically retrieve and import that info into its database.

A datafile is a special file that contains info about all games and ROMs supported by a specific version of an emulator. Logiqx's site is a great datafiles resource. He creates and maintains data files for many emulators, so there is a good chance you'll find what you need there. ROMcenter can import those data too into its database.
A “ROM path” contains the actual game files a user may have. They may be stored anywhere, either in a hard-disk, a flash drive, CD or DVD but for ROMcenter to be able to fix any abnormalities it may find in them, they have to reside in a writable medium.

Currently, ROMcenter supports only zip-compressed game files in a ROM path. If you find it useful, a ROM path may contain a subfolder for each supported game in which its ROMs will exist unpacked. In that case, ROMcenter may work faster, but you'll need a much bigger storage space.