If you are looking for open-source applications, GitHub is your best bet. Developers often compile their code into TPK files and release them in the "Releases" section of their repository. This is the safest way to get homebrew software.
Sites like the Samsung Developer Forum and XDA Developers host community-created TPKs for custom watch faces and utility apps. tpk file download for tizen
When you download a TPK file, you are downloading a compressed archive containing: If you are looking for open-source applications, GitHub