I have a lot of 3x3 regions (768x768) and there seems to be no option for that size. How would you make any size other than the allowed options using this?

This worked great. After all these years you got me to add a second region to my grid.

There were some questions about Regions.ini editor. The purpose is to provide a visual way to create/move regions. It is one HTML page so you can view source and copy and put on your own site, if you are in agreement with the license terms at the top of the HTML source. There are no php scripts, etc. You can optionally paste in your own Regions.ini and edit using the visual tool, and generate a new Regions.ini you can copy and paste into your OpenSim installation. It does not save your Regions.ini file on the server, it exists only in your own browser.It's not fully tested so please keep a backup of your original Regions.ini file before replacing it!