DeHashed - DeHashed is the largest & fastest data breach search engine.
Firefox Multi-account Containers - Sign in to two different accounts on the same site
Snusbase - The industry leading database lookup.
Lightbeam for Firefox - Mozilla is the not-for-profit behind the lightning fast Firefox browser. We put people over profit to give everyone more power online.
LeakCheck - Data breach search engine, low price starting from $10/mo, one email address for free, unlimited API, 7B+ entries
Multilogin - Connect to websites as a multitude of different users