I’ve just finished writing the big parts of usbscale, a command-line program written in C that reads and interprets data from USB scales. It was meant as a little hack for the Stamps.com scale, so currently it’s only set up to recognize the Stamps.com 10-lb scale (manufactured by Elane). It should be trivial to add support for more scales, though.
If you have a USB scale, please let me know!
You can find the software at usbscale on Github: https://github.com/erjiang/usbscale