What is it?

What if the MSX would have an USB connection? And if the BIOS/MSX DOS would automatically recognize devices connected to it?

Inspired by the work of Xavirompe and his RookieDrive, S0urceror started a project to do exactly that. Provide an USB interface to MSX computers. On his GitHub repository you can find:

Schematics (KiCAD), that interfaces a cheap USB CH376s board to the MSX cartridge port.
Drivers, currently Flash drives on Nextor and HID keyboards are supported.
Debugging tools, to connect a test board to your PC/MAC and assist in debugging.

Why did you make it?

What if your MSX had a USB connection? What if you could save your games to a regular pen drive and use them on your MSX?

Inspired by the work of Xavirompe and his RookieDrive, a group of friends have been working on a project to do exactly that. Provide a USB interface for MSX computers.

The main function of MSXUSB is to allow programs to be loaded from pen drives. Simply create an initial FAT16 partition on the pen drive, place your files on it and connect it to the cartridge's USB port.

If you want, you can also place the DSK files (disks) and mount them directly from the menu that appears when you turn on your MSX with the cartridge inserted.

The device also allows the LIMITED use of keyboards (only those compatible with the USB HID specification) and USB network adapters (only those based on the RTL8153 chip and that comply with the USB CDC ECM standard).

A switch on the cartridge allows switching between the firmware that mounts DSKs and accesses files and the firmware that allows the use of keyboards, network cards and any other device with a UNAPI driver developed for the MSX.

What makes it special?

The most practical function of MSX-USB is to emulate DSK disks. It can not only emulate traditional MSX floppy disks of 720k size, but also emulate disk images up to 128M, running sofarun just like a hard drive. In GitHub, this project has many BIOS options but lacks detailed introduction. After several days of sorting, I found the two most practical BIOS versions, both of which support FAT16/32 flash drives:
1.MSX-USB Next v0.5 20230520:
This version can easily run 720k dsk format disk games. After MSX is turned on, it will immediately enter the disk image selection interface. You only need to press the letters on the keyboard to select the file and start playing the game quickly. However, its emulation of 128mb hard drives is unstable. Even if it can emulate the entire FAT16 flash drive, the compatibility is very poor and sofarun cannot run normally. It can run some dsk format games, but it cannot run games that require switching floppy disks.
2.MSX-USB Nextor USB Host v0.5 20200615:
This version has perfect emulation function for large-capacity hard drive images. It can automatically emulate the "nextor.dsk" in the root directory of the flash drive and automatically enter sofarun when booting, just like a real hard drive cartridge. And it is fully compatible with sofarun, which means you can use it to play various ROM format games. You can manage hard disk image files on the computer, and you can also use commands to switch hard disk images on MSX.
As for other functions, I think they are not practical, such as limited support for USB keyboards, and USB Internet access is almost useless.