Devtest3 was meant to be a playable map in Unturned (version 3). It was originally planned to release alongside the initial NPC systems, but was never made public. The map can be seen in screenshots that appeared in announcements made around the time NPCs were still in development.
The map had entirely flat geography, with a couple of trees. At least three NPCs were present on the map, which would have showcased basic NPC functionality.