Sherlock is described as '🔎 Hunt down social media accounts by username across social networks'. There are three alternatives to Sherlock for Linux, Online / Web-based, Self-Hosted solutions, Android and Cloudron. The best alternative is searx, which is both free and Open Source. Other great apps like Sherlock are Profil3r (Free, Open Source) and Intelligence X (Free).
Profil3r is an OSINT tool that allows you to find potential profiles of a person on social networks, as well as their email addresses. This program also alerts you to the presence of a data leak for the found emails.