”The analytics has always been the foundation for us,” said Raj Aggarwal, Localytics founder and chief executive. “But over time, we realized that retention of users was a big problem in the app space.”

To solve this problem, the company has now publicly launched an app marketing platform which some of its existing customers have been testing for the past few months.

The platform can be used to help time coupons, discounts, and other offers in an application.

The early reviews were apparently positive enough to impress Series B investors to the tune of $5.5 million. Polaris Venture Partners led the round.

Aggarwal said that the Dogpatch Labs-housed startup, a 2009 TechsStars alumnus, would continue hiring and building out both its analytics and messaging platforms with the new infusion of cash.

Localytics first highlighted the retention problem early last year when it released a study that found over a quarter of of downloaded mobile apps are used just once.

Aggarwal said that rate was improving (closer to a fifth of installed apps are now single-use only), but many app developers were now hungry for new revenue streams.

Those that had counted on in-app advertising often found it never quite materialized, and are now hoping in-app purchases and other directed pushes can fill the gap.

The possible uses of Localytics’ app marketing tools range from offering discounts and reminders to asking them to share a piece of engaging content with their social networks, all in the names of increasing and spreading engagement.

”If someone is going through the purchase funnel, and he bumps out of the screen, it usually means they’re never going to finish their purchase, so we look at ways to get them back into the purchase,” Aggarwal said.

Combined with Localytics existing analytics tools, Aggarwal said his company can help mobile app makers discover if a 10 percent or 20 percent coupon provides a better return, and exactly when is the best time to offer those discounts.