Continuum is described as "a light-weight native OS X IDE for Mono".

It is hosted at  http://code.google.com/p/continuum-ide/ as an open source project. Written by Jesse Jones.

There is no specific Cobra support at this point, but Continuum has a pluggable architecture and it's open source, so it should certainly be possible.

If launched from the command line, Continuum may say:

WARNING: The locate database (/var/db/locate.database) does not exist.
To create the database, run the following command:

  sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.locate.plist

Please be aware that the database can take some time to generate; once
the database has been created, this message will no longer appear.

You don't have to create the "locate" database, but Continuum's "open selection" won't be able to find files and right-clicking on types won't let you open the associated file.

See also: IDESupport, EditorSupport