There is only one file type that uses the .TCCFGEXTENDER extension:
TestComplete Project Suite Settings File
Settings file created by TestComplete, a platform used for testing desktop, mobile, and web applications; contains settings for specific testing of a project suite.
NOTE: TestComplete uses projects and project suites to allow you to test different applications. Since you can test a variety of applications at the same time, TestComplete uses files, such as TCCFGEXTENDER, to hold test settings to maintain consistency.
Updated: February 6, 2015