- vEnhance (https://www.youtube.com/c/vEnhance), an MIT student and IMO Gold Medalist who solved problems live on stream (and plays various games)
- Osman Nal (https://www.youtube.com/c/OsmanNal), looking at problems ranging from AMC/AIME to IMO 3/6s
- Michael Greenberg (https://www.youtube.com/channel/UC3mhbGC7kQgzkXT9fceNOwA), a geometry enthusiast who also live solves problems, though the production quality isn't amazing
And of course, Michael Penn (but that's in the post above)!