Use OF 2 and OF 3 simultaneously

During the beta, I installed OF 3 alongside OF 2 on macOS and used a database snapshot for the beta.

I would now like to use OF 3.0.1 with my existing OF 2 installation’s database on the same machine, either by using the same local database or by synching to the same server.

  1. How do I get OF 3.0.1 to forget about the test database and
  2. what is the best practise to have both versions work the same database alongside each other?

Solution provided by @kcase on Slack:

The easiest way to sync OmniFocus 2 with OmniFocus 3 is to set them both up to sync their data with the cloud.

If you want to reset your entire OmniFocus 3 experience back to what you see with a fresh install, you can open the File menu, hold down the Option key, and choose the Reset Database and Preferences… option that appears about two thirds of the way down the list. That will remove your current database and prompt you to choose whether you want to keep your data synced in the cloud or start a new database on this device.