[Brian]

OmniFocus supports multiple databases, though there's no built-in UI for creating them.

Caveats: only one database - the one in
<your home folder>/Library/Application Support/OmniFocus
will be synced. Quick Entry will also only file into that database.

Just Quit OmniFocus, then open that location in the finder. Select the OmniFocus.ofocus database there, then File -> Duplicate from the menu bar.

Move the new database to whatever location you'd like, name it whatever you'd like, and open it with a double-click. Use the All Items perspective to clear out whatever the current contents are, and you're good to go from then on.

Hope this helps!