There's just one problem. If you've amassed a collection of Mac software over time, Apple doesn't offer a way to turn your existing app licenses into Mac App Store equivalents--and so far it has shown no intention of changing its tune.a "

A few Mac developers are riding to the rescue, however. A handful are finding ways to help users make the transition from the software they've already bought to the versions available via the Mac App Store. It's an encouraging turn of events, but one that's unlikely to sweep its way across the Mac platform. For some developers, the methods for moving their existing customers to the Mac App Store simply aren't tenable.

Over the past week or so, developers behind a handful of apps--many of them fairly new to the market--have announced offers to transition customer licenses into the Mac App Store. Those apps include Mizage's window management utility ; Irraddiated Software's Divvy competitor, ; and Victoria Wang's Twitter client.

Mizage and Irraddiated are using similar techniques: both companies sent out e-mails explaining that if existing customers re-purchase the respective apps and submit a proof of purchase (either by forwarding a Mac App Store receipt or sending a screenshot of the store's Purchases tab), they'll issue a refund for the original license purchase.