Groups was a fun and easy way to talk with multiple friends at a time with the commands `/g invite` and `/g msg`. It's like having somebody as a friend except being able to have many other people in it. When somebody in the group logged off, they also left the group. The groups were a temporary thing but you could always just create a new one with no strings attached.
I feel that this would not only be useful for talking to people in groups for fun but also an easier way for staff to help people. Say for instance somebody scammed/griefed somebody, well just add them to the group and then everyone can talk it out instead of messaging each person back and forth and sometimes losing track of things. Though they could refuse to join or cause more issues, if they were in that position, I think they would join.
Posted below are the features that groups bring, or at least, what they did bring. I would love to see this added back, it was an amazing feature back then and can be again.