Bforartists is a fork of Blender aimed at remedying Blender's often complained about interface, making it more intuitive. It should be noted the the interface for Blender 2.8 has had a big overhaul, and is pretty neat now!
- Level Buddy is a pay-what-you-want CSG-based level modelling plugin.
- Level Builder is a USD$20 plugin for composing levels from different blocks (you have to model the blocks).
Warnings / Workarounds
Blender and Godot
Godot doesn't get along so well with Blender's implementation of collada / .DAE files, but you can install the plug-in 'Godot Engine's "Better" Collada exporter for Blender' to get a better export.
I think for current versions of both programs you're better served by just export as GLTF2, see:
There's also a plug-in for exporting to Godot's native scene format:
Blender and Unity
Blender and Unity treat models a little differently: The forward direction is X in Blender and Z in Unity >:s
More info., and solutions in the guides section.