The Teensy 3.6 can act as a USB host. This includes support for class-compliant USB MIDI devices, as well as other types of USB devices.
The strength of this is to be able to use USB MIDI controllers without the need for a laptop or similar device, and can interface with Eurorack.
I've made a simple Eurorack module that acts as a USB MIDI host, and has two inputs that can be either gate or CV signals, 4 gate outputs and 2 CV outputs.
All of the relevant files can be found here: https://github.com/little-scale/eurorack/tree/master/USB_MIDI_Host
This includes an example for Launchpad Mini, PS4 controller, NanoKontrol 2.
Different USB MIDI devices have different Arduino sketches written for them as firmware. Each USB device has different controls, functions and mappings, and so the flexibility of having a USB Host module is weighed against needing to program each device.
I will be adding and updating this project in the coming weeks. My plan is to make a new PCB with buffered outputs, voltage scaling, and busses for IO expansion.
Here are demonstrations for NanoKontrol 2, PS4 controller and Launchpad Mini.