Rather than talking about any specific apps, let's talk about the type of app that could be useful! Photo editing is an obvious! There are hundreds of apps available that would allow you to edit an app however If you search around you will find some are geared towards adding comments to a photo while others are great for creating a collage and others might be dedicated to creating borders and backgrounds!
As a business owner, we found it very helpful to use apps that tell you who's following you back and who's not! We found it pretty helpful when we reached Instagram's limit if the number of people or other Instagram accounts you're able to follow.
There are even apps like Hoot Suite they would allow a user to create an account and attach an Instagram account. The app is used to manage several social networking or social media accounts at once, most tools like this do not include Instagram! Hootsuite will give it's users real time notification from several networks at once, the ability to respond to any notifications, it even let's you load your media and post it at hot times of the day and or to several networks at once!
Although Instagram is great for messaging and communicating, and they also added direct message or DM features there are numerous apps available providing private, and or instant messages which are commonly used by Instagram's users.
Search around and see which marketing tools might be best for you! As always visit www.simplemediamarketingsolutions.com for your marketing needs!!