Outside the "basics", I've seen Newton's method come up again and again in my work. I also work on some map software and geometry (especially trig) has been really useful.
I think using slack asynchronously (and developing norms that support it) is useful. Also imo there's an unspoken tradeoff when you work for a full remote company across time zones. Most workers seem comfortable with trading the convenience of remote work for the possibility of getting pinged outside work hours.