Steam has two semi-related features for this, but neither did what I wanted. You can click on a single user's profile and see what games you both have in common

Steam has two semi-related features for this, but neither did what I wanted. You can click on a single user's profile and see what games you both have in common, or you can click on a game you own and see what other friends own it. This tool is just an extended version of that first feature to work with multiple users instead of just one. I made this to solve a niche issue me and my friends had, where none of us knew exactly what we wanted to play, and each game we suggested wasn't owned by everyone. The name "What Can We Play?" is actually the phrase I've said every time this situation came up.