Marketcircle has released Billings Pro 1.1 with support for QuickBooks and MoneyWorks. Biliings Pro (our review) offers time tracking, invoicing and billing for small businesses and groups. With support for multiple users, server software and client side applications, Billings Pro is a nice solution.
This update lets you export clients, invoices, payments and more to an IIF file, which can then be imported with QuickBooks (it goes in the other direction, too). Likewise, it'll exchange data with a MoneyWorks database.
They've also made general performance a bit faster. You'll find upgrade instructions here. Note that you've got to update both the server and the client, so it's a bit trickier than double-clicking an installer and sipping a latte.
This is a free update for registered users.