Phplist and OpenEmm are both free mass mailers. They send your mailing lists/spam to your customers/contacts/harvested lists.
OpenEmm = more features + complexity in options + prettier OU
Phplist = more simple + technical
OpenEmm is not Phplists big brother or anything, its just ummmm.. Different..
Both are heavily customizable with a little code knowledge..
Anyway this is just a quick brain dump..