Mac OS X: Twitter's free client for Mac has received its first major update today, giving users the ability to view multiple timelines at once. Other improvements include easier navigation and auto-completion of both hashtags and usernames.
Viewing multiple timelines happens in multiple windows, unlike TweetDeck, which uses columns inside one large window. Navigating back through timelines is now easier due to a bar at the top of each window, and they've also added a "New Tweet" button to the main app window.
It may have taken a (very) long time, but the addition of username and hashtag auto-complete is definitely a welcome one. Direct messaging is now more conversation-like, and another nice but small change is for user profiles, which can be viewed more easily while staying inside the app.