Rolling multiple attacks & saves all at once for groups of NPCs or monsters. Generating random monsters and treasure items. Generating names for many things - npcs of different races, dragons, books, towns, inns, etc. A lot of the randomizing can be done with AI now, but using mine is faster, and it creates names that sound culturally consistent for my world, using parts of names and rules for combining them. I can construct a pretty decent new generator in like 10 minutes.

I also have a Discord bot that maintains parties, keeping track of everybody’s XP and level. I put in the total XP for a game session, and the bot does all the arithmetic to distribute it amongst the party, factoring in multiclassed characters and those who get a 10% bonus for high ability scores (this is for 1e/2e AD&D campaigns). I can also award individual XP for outstanding deeds etc.