I think that the quests you get in diamond city's wanted board and those from the Valentine detective agency are radiant. Theres probably more spots to get these kind of quest.
Yes theres a few within the factions, and there actually quite rewarding, I'm getting more caps with them then anything else.
Preston gives you them as "save this settlement" kind of quests. Very rewarding for loot and caps
There are a few radiant quests, but they are not that much in your face missions. Like in Skyrim your quest log was just updating all the time and full to the brim with crap. Here its abit more contained. There are some repeating faction missions, and bounty missions.
As others have mentioned, there are quite a few radiant missions. One interesting point with them is t hat they often force associated buildings to respawn entirely, including clutter objects. All those fans, phones, and typewriters will respawn. This is very handy for salvage!
Preston will ask you to save a settlement like every other day, I was like how can I remove the settlements. I hate saving them from raiders all the time that is why I built 10 turrets
to protect them. Also Brotherhood of Steel has go here wipe out the infestation of lesser beings or go find some piece of tech, the railroad has go raise the defense of this settlement
to place a safe house there and go rescue this synth, not sure about the Institute I haven't done much in the way of assisting them outside the main quest missions.
Yeah, the game throws way too many settlements at you too fast if you hang around Preston at all... BUT, there is a way to get rid of most of them! You can go to normal settlers and tell them to 'move' to another settlement. This doesn't work on named settlers, but only a few of the settlements come with named settlers. The rest can been discontinued with their settlers consolidated in your main settlements. I wish I had known this early on. I've been going through later and consolidating, but that's after I've wasted resources setting up food, water, and defense... AND responding to random distress calls that get annoying. I've lost count of how many colonies I have... toooo dang many for sure.