Polygon Crest – open-source 3D polygonal editor
ysflight.in.coocan.jp
ysflight.in.coocan.jp
Sources distributed with binary builds, but recent code hosted on GitHub.[1]
This 3D editor support parenting & linking mesh parts (SRF) for creating assembled animation models (DNM).[2]
Additionally to supporting OBJ, STL and OFF mesh formats, Polygon Crest use own file formats (DNM & SRF), which in some way similar to AC3D format.[3]
[1] https://github.com/captainys/public/tree/master/src/ysgebl
[2] https://twitter.com/app4soft/status/1251227413570375680
[3] https://forum.ysfhq.com/viewtopic.php?f=147&t=8172&p=92286#p...
But if you never tried to create addons for YSFlight, then, off course, its look not suitable for your needs.
As for me, Polygon Crest is nice part of 3D modeling software and I keep it in my toolbox side-by-side with Blender, Maverick Model 3D & Wings3D polygonal/mesh editors.
[0] https://twitter.com/StarGear_TII/status/606719540068646912
[1] https://twitter.com/StarGear_TII/status/606719540068646912