Twitly
The good news is that several services besides Twitly are trying to provide this feature such as TweetDeck, GroupTweet and TweetParty. However, I think the simplicity of Twitly gives it a slight edge over the competition and possibly ripe for purchase by Twitter (who recently bought summize for their search solution, which still isn’t linked to their home page but I won’t go there!).
Simply login with your twitter credentials and create the groups you want and start adding your tweeps!
That’s all there is to it. You can go from one group to the other with a click of the mouse, no messy client to download and install or special new twitter ID to create and possibly risk exposing private DM’s with the world. Just create a group and add members.
Suggestions
Twitly is new and will add more features with time of course. One of the things I would love to see is the ability to provide public groups that anyone can join (pending approval from the group leader if that is needed). As it is now, all of our groups are private and manually managed ourselves which means we have to add/delete members. It would be nice if Twitly used the same concept that FriendFeed does with rooms.
We need to be able to make our groups private or public.
Conclusion
I think we’re moving closer to the holy grail of having true groups on Twitter thanks to services like Twitly and the others mentioned.