>>24181
Thanks for that link. I know one: Prototype. It's the free version of ProBuilder (or similar name) and it's practical if you need essential shapes like stairs and door frames. It's pretty good for people who don't need detailed geometry. You can manipulate the basic shapes by a few parameters like number of stairs in the case of stairs, stuff like that, and you can move every edge and point around. For instance you could turn the basic shape pipe into a mosque roof by closing its top.
Problems: There can be compatibility issues, I don't know how well it's supported. I'm still on 5.0.1 or something. Pic related is the kind of bug you can expect. Usually saving and restarting Unity fixes this. Also the objects created with it come with a custom collider that has a script attached. I've found that for instance deactivating that collider by removing the unchecking it in the inspector won't work, it will turn back on moments later. You can't remove the collider component either. Maybe you can fix everything by altering the script, I haven't tried that, just thought I'd mention it.
I would advise everyone to try Prototype out but I would warn you to become well acquainted with it (better than I have) before relying on it for more than its name suggests.