With OUI Lookup you can figure out who manufactured a device simply by inserting its MAC address in the search bar.
You can also search for a manufacturer and see its assigned OUIs.

Features:
Trusted source - The database is sourced from the IEEE to be as correct and updated as possible.
Works Offline - OUI Lookup works completely offline, an internet connection is only needed to update the database.
Bulk lookup - You can paste a comma/semicolon/whitespace/new line separated list of MAC Address