For railroad the quest 'Underground Undercover' marks the point of no return. The others points of no return are pretty obvious, you'll be prompted to go and kill said factions, so don't do it if you have stuff to do beforehand. This is also true for a variety of other quests, like Pinned, though some ways of handling them may require successful speech checks if you want to remain friendly with everyone.

For the BoS the quest “Liberty Reprimed” is the point of no return.