Unix security tool. Official description: "AIDE (Advanced
Intrusion Detection Environment) is a
free replacement for
Tripwire. It generates a
database that can be used to check the
integrity of files on
server. It uses
regular expressions for determening which files get added to the database. You can use several message digest
algorithms to ensure that the files have not been
tampered with."
Note that
tripwire is now
open source, and thus free. Perhaps the biggest
advantage of using AIDE is that it's not as well-known as tripwire.