Biz Stone’s mysterious startup Jelly has just made another interesting hire. This time it’s Brian Kadar, a former Apple software engineer.

Here’s what Stone had to say about Kadar:

“Born and raised in Queens, NY, Brian has a BFA in Visual Communications which he decided to use as a backdrop for pursing web development. Before Apple, Brian built experiences for brands at a boutique advertising agency in NYC. Ben and Austin were lucky enough to be introduced to Brian through a mutual friend. Before I’d even had a chance to meet him, Brian started building some amazing mobile web experiences based on the basic concept of Jelly.”

This isn’t the first ex-Apple engineer Jelly has grabbed recently. In June, Jelly announced that they had hired Loren Brichter, a former Apple engineer who worked on the original iPhone. He also spent time working with Twitter, where he developed the “pull-to-refresh” user interface mechanics patent.

Other high-profile hires include Mac OS designer Austin Sarner and Twitter’s Ben Finkel as CTO (he also co-founded the company).

That’s a bunch of interesting hires, sure. But what exactly is Jelly? Stone has been very careful not to reveal anything. We know that it is a primarily mobile-focused app, and signs point that it may have something to do with “social good.”

“People are basically good – when provided a tool that helps them do good in the world, they prove it. Jelly is a new company and product named after the jellyfish. We are inspired by this particular animal because neurologically, its brain is more ‘we’ than ‘me.’ Also, for the past 700 million years, this decentralized structure has been wildly successful,” said Stone when he announced Jelly back in April.

In May, Jelly announced that it had closed its Series A funding, lead by Spark Capital with investment from SV Angel. They also disclosed some early investors and it turned out to be a rather interesting list – names like Jack Dorsey, Bono, and Al Gore.

Whatever Jelly is, we won’t know for some time. Stone has said this himself. But they are building a talented staff, that’s for sure.