If you want something similar than ZBrush or 3D Coat (for modeling polygonal subdivision) but "free" take a look at Rocket 3F!

Very cool Interface (like Moi ;)

And it has a direct "bridge" between Moi3D and Rocket 3F in the 2 ways!
https://moi3d.com/forum/index.php?webtag=MOI&msg=8092.101

@ Michael:
Yes, could work. Must try that out. Perfect I guess. The tutorial is great. I´l give feedback...
@ Pilou:
Thanks for the idea. Try it out with MOI. And perhaps I switch to your tip...
Salut, M.

I made progress, I think.
But I cant stitch the element together. Did I work not properly?

seems the object Super Rinne is an only one object!

Thanks for looking. Not sure what´s the consequence of your statement...
But I remodeled it and I could stitch the elements now.
Thanks for your tipps and very nice help - Pilou and Michael!!!
Salut, MaLa

P.S.: Next project I´ll try to find out what the difference for stitching is using Boole or Connect Tool...

What method have you used for success your stitching ?

Have a look at the videotutorials from chippwalters.

This covers your problem nicely:
https://www.youtube.com/watch?v=2-5J6hLRDaI

Easy peasy.

Indent/outdent. Just loft the surface with the kink in it, instead of trying to add it later...


Top, straight surface, and curved, outdented...



Bottom, indented...