You can attach all kinds of files, like photographs and videos, from within the application or from the directory where they're stored. Then you can manage and integrate other social networks with your tweets, like Facebook and Foursquare. You can also manage various Twitter accounts from the client, adding as many columns as you wish.
Some other interesting features allow you to see statistics from your Twitter account, for example which countries your followers are from, or who follows you that you also follow.
On Facebook, you'll be able to monitor and manage your Facebook pages, update statuses, and upload photographs. If that weren't enough, HootSuite also allows you to check on your LinkedIn profile.
HootSuite is easily one of the most comprehensive clients for Twitter out there. That's because it's much more than a simple Twitter client... it's a mobile social media client.