Apps similar to 7thAmigo include Instant Username Search, which is free and open source. Other options are 360username and Chirp.blue. In total there are three apps like 7thAmigo for the web and self-hosting.
Instant Username Search is a free and open-source web app to check if a username is available on services like Facebook, Instagram, Reddit, GitHub and much more. It's available online or as a self-hosted app.
360username helps you find, check, and secure the same username across the internet. You can instantly search your preferred name across more than 90 platforms to see where it’s available.
Elon Musk tweeted that Twitter is finally going to purge inactive accounts. This means that you can finally get your desired handle, but you have to be quick!
