Over the last year, a firm called Usergrid has been building an open source tool for leading mobile app developers through the process of creating back-end services for managing users. The Usergrid philosophy is contrary to quite a lot of the cloud-centered design methodology promoted by SaaS - the idea that the server can do everything, and a thin device can serve as the portal. Instead, Usergrid has promoted the idea of richer mobile apps that use Web services and APIs in a more passive, RESTful manner.

Late last year on its company blog, Usergrid stated its intent to build out to a cloud-delivered service - essentially, transferring its intelligence to the cloud to help devs build intelligence on client devices. This morning, the firm got its wish, though maybe in a way not everyone expected: Usergrid has been acquired by cloud-based API modeling tool provider Apigee. And as both companies' CEOs tell ReadWriteWeb, the fruit of their new relationship is a little ways down the road.

"The goal for Usergrid is to be able to provide the developer with an instant mobile back-end stack," explains Ed Anuff, who up until today was Usergrid's CEO. "Most mobile apps need a cloud back-end that provides them with a lot of their key capabilities. Mobile apps are user-centric, they're data-driven, and they need to be powered by a highly scalable back end." For example, mobile apps need standardized connections with social networks, not just to share content and compare social graphs but to authenticate identities.

"When a developer looks to use a mobile back end, it saves maybe 80% of the cost of developing an application," Anuff remarks. "Otherwise they'd have to do that all themselves."

What will a pairing of Apigee and Usergrid accomplish that Usergrid wasn't just about ready to do on its own? "First, it's going to allow us to get this to market in a faster way," responds Anuff. "We're going to be able to deliver it as a cloud service, which was our goal in the launch of Usergrid. Mobile app developers want this to be a seamless, one-click experience. With Apigee, there was a common vision in the way that APIs should be built and consumed."

During Usergrid's last round of beta testing, Anuff reports, the amount of API traffic generated by mobile apps was staggering, even compared against the firm's own expectations. Building on Apigee's existing platform could provide Usergrid with the more robust service performance its testers have been looking for.

But does this acquisition lead to a single Apigee tool, going beyond simply accessing and modeling API functions to the point where developers could instantiate them, populate them with user data, and modify them until they're in proper working order to include with their own mobile apps' source code? This is a question that Apigee CEO Chet Kapoor deferred for a while, though the tool for his deferment looks curiously like a velvet curtain wrapped around a gift-wrapped box tied with a bow.

"Stay tuned," Kapoor responds to RWW. "We understand the problem really well, and it's something that we're working on. Having Ed join us is going to accelerate those plans in a big way."

Some of the problems Apigee had been working to address, even before this morning's Usergrid acquisition, deal with the rapidly expanding and splintering nature of APIs themselves. They're changing almost too fast for any one service to keep up with, which in a sense mandates the need for a kind of Apigee cloud app that works in reverse - absorbing new API functions from their own developers, so app devs can work with them right away. That's an infrastructure problem that Kapoor confirms to us his company has been working with, saying, "We're going to make that infrastructure available very soon."