Userhunt.co Username search
If you're a fan of the open source tool Sherlock, there's great news. UserHunt is a GUI built on top of Sherlock and allows you to get the same results without running scripts in the command line. This is great for people operating mostly within a browser and with limited desktop space; additionally, it's great for the low-tech OSINT investigators as well. This is by far the cleanest user interface I've seen on a username check website. Make sure to bookmark this if you're already using Sherlock.