TAR does one job: it glues many files into one, preserving Unix permissions and structure. It compresses nothing at all, which is why it is nearly always paired with gzip. It is the standard way source code and Linux software move around.
Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a TAR file above and choose afterwards.