SuperSU is an app that any rooted user will know, even if you don't use it. I have fond memories of it from my days rooting and ROMing every device I could get my hands on, and it would appear that I'm not the only person who feels this way — SuperSU just hit the impressive 100 million downloads mark.
If you don't know, SuperSU is an app to manage the root functions on your device. Most people use it for seeing a list of everything that has requested root access, regardless of whether you allowed it or not (you can also change that root permission decision there). There's the ability to customize notifications, toasts, prompts, and many other quality-of-life features, too. Until recently, it was my personal root go-to (after flashing the supersu binary).
If you'll recall, developer Chainfire sold off the application to CCMT almost two years ago, saying that he would continue to work with them on SuperSU's development for, well, two years. The time for that cooperation is ending quickly, though. Hitting the 100 million mark is no small feat, so congrats to Chainfire and CCMT. Magisk may be my default root solution now, but I will always remember SuperSU fondly.