SocialOomph
Formerly TweetLater, SocialOomph has the oft-reviled “auto-follow” functionality. Auto-following may be out of vogue with the tweeterati, but for some marketing initiatives, it is still the most appropriate policy.
SocialOomph is missing the strong team management capabilities of the above platforms, but they are the ultimate solution if you are a one-person show. They also have an annoying layout, with precious screen real estate taken up by a banner ad recommending someone for you to follow, and a left nav that has a narrow font and low contrast, making it tough to read. While the back-end coding is solid, the usability of SocialOomph is hampered by these annoyances.
Where SocialOomph excels is in campaign planning. All services offer a scheduling functionality to send your Tweets later. But, SocialOomph goes one step further, by offering a queue feature.
You can create a queue around any theme or idea, e.g. “links worth sharing,” “retweets,” or “registration reminders.” Each queue has it’s own automated publishing schedule that you determine, e.g. “every 12 hours,” or “every 15 minutes.” Then, you can feed multiple queues into one Twitter account.
This is powerful because it allows you to conceive of a persona for your account, and ensure that the account behavior is useful for the target audience; and their “email when dry” function makes it easy to see when you need to get cracking and create some more content for a queue.
Cost: SocialOomph has a free plan, which is fairly limited, and a pro account that costs around $30 per month.