Apps with 'MIME Types' feature

Default Programs Editor is a powerful but simple file association utility for Windows 7, Vista and XP. This free utility has three main functions: context menu editor, auto-play editor, and default programs association editor.

FileTypesMan is an alternative to the File Types tab in the Folder Options of Windows. It displays the list of all file extensions and types registered on your computer.

RCDefaultApp is a Mac OS X 10.2 or higher preference pane that allows a user to set the default application used for various URL schemes, file extensions, file types, MIME types, and Uniform Type Identifiers (or UTIs; MacOS 10.4 only).