TecAlliance offers official mobile apps. While they may require a login or "credits" for heavy use, they provide the "portability" many users seek by allowing you to scan VIN numbers or search for parts directly from your smartphone while under a car. The Bottom Line
Here is the hard truth:
If you only work on a specific brand (e.g., VAG group or Mercedes), you can create a portable database yourself. tecdoc online catalog free portable