Today I was presented a scenario where a client wanted to integrate a non-Microsoft Office desktop application into their Microsoft Office SharePoint Server 2007 (MOSS) environment such that documents created/edited in that app and stored in MOSS document libraries were able to be directly opened into that app ready for editing, and ultimately saved back to the document library.
Since Google'ing the answer to this scenario took me more than 30 seconds to find, here is the answer.
Inside SharePoint - Integrating "Office" Applications
And here are some more useful links:
Text Files, Associations, and SharePoint
Sharepoint Beef #3 : Melt-in-your-mouth Native Apps support issue resolved
How to enable the “Edit in Microsoft Office XXXXX” feature for Office 2007 documents
DocIcon.xml - Adding Notepad and WordPerfect as applications
Adding a Document Template, File Type, and Editing Application to a Site Definition
PDF Integration in SharePoint
Customizing the Shortcut Menu for List Items
Customizing SharePoint Context Menus