CH341

https://www.wch-ic.com/products/CH341.html

https://github.com/harbaum/I2C-Tiny-USB

The existing linux code for it appears to be based on a decompiled windows drivers. The best source for these appears to be https://github.com/command-tab/ch341eeprom/tree/master. Specifically https://github.com/command-tab/ch341eeprom/blob/master/ch341docs/CH341DLL.H pulls out most of the constants from the DLL and https://github.com/command-tab/ch341eeprom/blob/master/ch341docs/CH341EVT.ZIP appears to be the actual DLL itself (though the files are obviously not UTF-8, yay, mojibake).

https://github.com/frank-zago/ch341-i2c-spi-gpio/tree/master seems to work (mostly!)