Twitter separates tweets into categories using "hashtags," keywords that start with the "#" character. However, hashtag searches are broad and don't emulate the groups on social networking services like Facebook, or the "newsgroups" that were the heart of the early Internet. If you want to focus the tweets you receive onto a specific topic or community, you can use any of several free third-party services that allow users to create and join Twitter groups similar to those from other social networking services.
Use the site "Twibes" to find Twitter groups that share your interests. The site allows any Twitter user to join a group, called a "twibe," simply by sending a tweet that includes the URL of the twibe's homepage. After you join, any tweet you send that includes the twibe's keywords will go to all members of the twibe. Likewise, you'll receive any tweet from other twibe members that uses the same keywords.
"Twittgroups" is a service that's similar to Twibes, but provides a "wall" space for group members to post on via Google Friend Connect. Twittgroups designates a Twitter hashtag for each group, provides a list of group members, and collects links tweeted by group members. To join a Twittgroup, follow the link in the Resources section to the Twittgroups homepage, find a group that interests you, and then click "Join." Fill in the form with your Twitter ID (not password), real name, and the URL that's listed for the group.
Twibes and Twittgroups collect tweets from group members, but the tweets themselves are still generally public and. "Grouptweet" is an alternative that allows Twitter users to create private networks, so that tweets within the group are seen only by group members. The creator of the group sets up a single Twitter account as the hub, and you join a group by following the hub account. Any tweet sent to the hub automatically gets bounced back to all the followers. The group creator can make the group private by setting the hub account to "protected," so that the group manager has to approve you before you can follow the account. If the hub is protected, only the group members will be able to read the group tweets