GinormoTime includes a built-in Linear Timecode Generator, which can output LTC (also known as SMPTE TimeCode) using your PC's sound card or USB audio interface.
GinormoTime is completely free and only requires .net framework 4.7.2 or higher to be installed.
GinormoTime's LTC Generator is fairly rudimentary, if you need features that it doesn't provide then you may consider one of the non-free but more capable offerings.