This post is part of the Who's @ Google I/O, a series of blog posts that give a closer look at developers who'll be speaking or demoing at Google I/O. This guest post is written by Amit Kulkarni, Co-Founder and CEO of Manymoon, who will be demoing as part of the Developer Sandbox.

Manymoon is a free social productivity tool that helps teams manage and share projects, tasks and conversations. We became part of the Google Apps Marketplace at launch and have seen tremendous early success. Over 1,000 new businesses sign up each week, making us one of the top apps in the Marketplace. Below are some of our tips for building a successful app:

1. Define the problem - and make sure it's a big one!
For us, that was all the communication that gets lost in email. We thought email is great for notifications and is great ... as of 10 years ago.
But the internet is now social and about communicating for fun and work and both! And Google Apps has 25 million users and is signing up over 3000 new businesses a day.
We realized there was a significant opportunity.

2. Simplicity Sticks
Building a web app is different than building an enterprise app. The premium is on intuitiveness and ease of use. You've lost if the user has to read a manual, FAQ or go through a tutorial. User attention spans are short and it's critical for them to get up to speed in minutes. And that meant starting with something very simple: sharing tasks and projects.

3. Focus on What You're Great At
While in private beta, we had numerous customers asking for the ability to add documents to tasks and projects. The more we discussed with customers the more we realized that they were asking for features outside of our core vision. For example, they were asking for things like version control and co-browsing. This would have taken us months to build and is a whole different startup in fact! Instead, we decided to integrate with the Google Docs APIs. From a technical perspective, it provided us with the features our private beta users needed and it only took us a few weeks to complete! We immediately saw significant traction with users since our daily visits increased by 300%.

As we receive feature requests from users, we always look to see how we can integrate existing Google Apps to provide a better user experience. Another great example is our calendar feature. Customers were asking for a graphical calendar feature that included all necessary project information: open tasks, events and milestones. We were able to use the Google Calendar API and in just a few days provide this feature to users. We did this by using the API to automate multiple steps: create a calendar, share it with people and seamlessly update it with the latest project information.

4. Re-Use and Drive Engagement
One major benefit of using Google APIs was the way it reduced the friction to get users engaged. We did this by re-using each user's existing data in Manymoon! Specifically, a user can use Manymoon for tasks and projects that immediately work with their existing Google Docs, Google Calendars, Google Sites and Google Accounts (including OpenID). This dramatically reduces the barrier to the user trying a new app and increases relevance (since their existing data is available within the app).

We're presenting at Google I/O next week where we'll share more tips on this topic in our session, Reach new customers fast: Learn how to sell your cloud app on the Google Apps Marketplace. We’ll also be in the Developer Sandbox and would love for you to stop by our station and share any questions, tips or tricks.