About the spawn.dfn:
It is based of the spawn.scp from Ripper's World for the Lonewolf EMU. It was then converted by me into the UOX3 spawn.dfn format and cleaned up a bit. After that Fresshness and I added another bunch of spawn regions to it, so that the world is now quite filled with NPCs, creatures and reagents. See https://www.uox3.org/forums/viewtopic.php?t=434 to read up on it.
What it does:
It currently spawns most of the npc vendors to the towns, some random folk and pets in the town of Britain, some farmers and farm animals in the farmlands, many different creatures to the outside world and dungeons, and reagents all over the world. But it still isn't complete, better see it as a good starting point and adapt it to your needs.
Customizing or improving it:
To easily modify the type of creatures spawned in the different regions you can edit the npclists.dfn in the npc folder. To edit single spawn regions or add new ones I would advise to use mspawnf v1.2 Xuri posted over here.
It also would be nice if you post any improvements or custom made versions over here, so it can become a really good default spawn file.
Community-made Spawn Download
Download: https://www.uox3.org/files/community_made_spawns_v2.zip
GitHub Repo: https://github.com/UOX3DevTeam/UOX3-Resources
Thanks to everyone involved into creating the spawn.dfn and the UOX3 team for this nice emu.