A script that automatically sends you a PM me with any threads you were mentioned in would be good.
I'd also like a script that adds a chatbox to the site, allowing users to casually chat with one another.
It doesn't send PMs but there is this "Maggiordomo" bot that posts in your "mentions" thread or send you a message on Telegram everytime you get mentioned/quoted.
[RELEASED] @mention notification bot - now with Telegram