You can spice up your singleplayer game while your friends are playing different games with Archipelago!

What is Archipelago?
>Archipelago is a cross-game modification system which randomizes different games, then uses the result to build a single unified multi-player game. Items from one game may be present in another, and you will need your fellow players to find items you need in their games to help you complete your own.
https://archipelago.gg/
https://archipelago.gg/faq/en/

Currently it has support for 76 games, for this thread there's DOOM I, DOOM II and HERETIC.
https://archipelago.gg/games

>How to setup?
All three use a modified Crispy Doom named Archipelago Doom (APDoom). There's server chat you can use and !hint command to know where your next progression item (map unlock or key).

https://archipelago.gg/tutorial/DOOM%201993/setup_en
https://archipelago.gg/tutorial/DOOM%20II/setup_en
https://archipelago.gg/tutorial/Heretic/setup_en

Have fun!