The .mct file extension is most commonly associated with the Windows Live Messenger application. The MCT files contain packaged "wink" files that are used by the Windows Live program. "Winks" are flash animations that are used to convey emotions in IM conversations. Some MCT files are provided free with the Windows Live software while others can be purchased online from third-party vendors.
The .mct file extension is also used for Musicator MIDI files and MapChart genetic map data files.
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If you have additional information about the MCT file format or software that uses files with the MCT suffix, please do get in touch - we would love hearing from you.