OBS is widely used video recording and live streaming software. If you're looking at a Youtube video or a Twitch stream where multiple streams of video are over

OBS is widely used video recording and live streaming software. If you're looking at a Youtube video or a Twitch stream where multiple streams of video are overlapped with one another, e.g. the commentator is in the bottom corner while the commented content covers the rest of the screen, you're probably looking at OBS.