Open source 

• 30b -- 30boxes
• Celly -- for watching incoming Twitter messages
• Demeter -- a Shiira 1.2-based browser
• Dofex -- a WebKit app for the MMORG
• Dom announces Odeo.app -- Odeo app
• Gcal -- Google Calendar
• Gmail Browser -- by Ben Willmore
• Gmap (zip) -- Google Maps
• Greader (zip) -- Google Reader
• Hiker -- an app for Backpack
• Hotmail Browser
• PandoraBoy  (Mac OS X Downloads) -- for listening to Pandora with global hot keys and Growl integration.
• PandoraMan  -- for listening to Pandora
• PandoraJam  -- for streaming and recording Pandora
• Diet Pibb.app by Chris Messina for the group chat website pibb.com
• Pedia.app (MacUpdate) -- simply Wikipedia app
• Streampad -- streaming iTunes replacement with Archive.org integration
• Tominated Browser -- a general browser
• VibeKit -- NetVibes
• WebDesktop -- a transparent WebKit window that sits on top of your desktop picture
• WebMail (tgz) (read more: Hawk Wings, Michael McCracken, McCracken follow-up)
• YourMinis (zip) -- Goowy web-based widget desktop 

Proprietary 

• Fluid
• Direct URL
• Hana
• Mailplane