There are front-ends, such as majorcool, to provide a web interface. Many mailing lists are still run using majordomo.
Most, however, moved to commercial mailing list hosting services, often with a stipend of $100 or more paid to the list owner by the hosting service in exchange for the transfer. Most of the hosting providers were subsequently bought out by Yahoo. They are still present as "Yahoo Groups."
Before Majordomo, mailing lists were maintained manually, with a list owner adding and removing participants by editing a text file.
A commercial product used during the same era is Listserv.