The Technoethical Nano OTG Adapter is a very small device, that makes it possible for the regular USB A devices to be used with Replicant phones, such as the Technoethical S2 and S3.
It has a male micro USB B connector at one end, and a female USB A connector without the metal support/shield, on the other end.
This way, you can plug an external Wi-Fi USB adapter, so that you can use high-banwidth internet in freedom. Technoethical N150 Mini is the smallest, so the most convenient, and Technoethical N150 HGA is the solution for having an external Wi-Fi antenna connected to your Replicant phone. Other ath_9k-htc supported Wi-Fi adapters should work, since they are compatible with free operating systems.
Aside from that, any USB device should work, provided that they have completely free drivers, and those drivers are included in Replicant.
Write to us if you think that one unsupported device might be useful to phone users. We'll do our best to help having it included in Replicant.
You can also connect the adapter to a normal data/charging USB cable (A-male to micro, or other configurations), and then to be able to charge other devices from an OTG-compatible phone.
The only USB devices/cables that are not physically compatible with this adapter are the ones whose USB A male port also doesn't have a metal support/shield.