It's the same software used by the official Linux Kernel Mailing Lists: https://lore.kernel.org/
- It lets people `git clone` the archives and then `git pull` from them incrementally, so you get the same "distributed backups" that git provides.
- It also provides high-quality (Xapian) fulltext search, RSS/Atom, and NNTP access.
- It doesn't artificially fracture mailing list threads at month boundaries. I know this sounds like a trivial feature, but I'm constantly astonished that most other mailing list archive software does this. It's so irritating.
- Most important of all, it provides a smooth migration path away from SMTP-push for mailing lists, which has always been the big headache. Most of the problems with email go away when you switch from push to incremental-pull. Unsurprisingly, git is the perfect tool for doing incremental pull.