These are the normal Tinderbox files in which user data is kept.
Filename Extension: '.tbx'
Icon: White page with the flame from the Tinderbox program icon and 'TBX' beneath it.
New Tinderbox files default to having a '.TBX' filename extension. This is not shown in the file save dialog but as added as part of the initial file save. The extension will show in Finder and within Tinderbox window titles on any subsequent use.
It is to be presumed the '.TBX' extension will also be used as the program's data filename extension for the Windows version, when it arrives.