Is there a board that can act as both a USB host and client for HID devices? Trying to build an arduino-based Mouse/Keyboard enhancer.  This will let me do things like press certain keyboard or mouse shortcuts on the input side, then do something custom on the output side.  For instance, this would let me add keyboard shortcuts at the hardware level instead of having to do them at the OS level.

As such, I'm looking for a board which can act both as a USB host (i.e. it can have a keyboard and mouse plugged into it) as well as one that can show up as a USB HID device to the computer it's plugged into.

The boards that I'm aware of which have something close to this are the Leonardo and chip-similar, which work to emulate a keyboard/mouse to the computer they're attached to, but which don't let you connect a keyboard/mouse to them.

So is there such a board?
The TMK USB to USB converter is a thumb drive sized board with ATMega32u4 and max3421e with pass through/remapper software. It has the same functionality as a Leonardo with USB host shield.

https://geekhack.org/index.php?topic=69169.0