There is only one file type that uses the .TCNET extension:
TestComplete Configuration Reference File
Configuration reference file created by TestComplete, an application that enables users to test applications; contains references to configuration files for a project or project suite that is being used in shared mode.
NOTE: TestComplete uses projects and project suites to allow you to test different applications. You can test applications using shared projects, which allows multiple users to work on the same project. TestComplete uses TCNET files to maintain the same configuration for projects or project suites.
Updated: August 26, 2014