- Copy your Notational Velocity application (so it's called "Notational Velocity copy" or whatever)
- Adjust the key in the info.plist of the package so that the CFBundleIdentifier points someplace different (e.g., net.notational.velocity2)
- Launch the NV copy and adjust the notes directory to also be something different
That's it! Now you've got two Notational Velocities running side by side. You can even give them different hot keys and different fonts so you can tell them apart.
I think the same thing would work with nvAlt, which by the way will sync your tags to simplenote, which is a big deal.
Check out the mini-discussion with heavy-weight Superuser @Lri and a
cleaner solution using defaults write and ditto.