This is the Sublime Text package that provides syntax support for the TADS 3 language.
This package can be installed via Package Control for Sublime Text under the name TADS3.
You may want to associate the .t extension with the TADS 3 syntax. To do that, open a file with that extension, click the syntax name in the bottom right corner of Sublime Text, and choose Open all with current extension as... | TADS 3.
This package is in the public domain; see the UNLICENSE file or https://unlicense.org for more details.