<i>ykDroid</i> is a USB and NFC driver for Android that exposes the challenge-response feature of YubiKeys for use by other Android apps. Both USB and NFC (YubiKey NEO required for NFC) are supported on compatible devices. Apps supporting it include e.g. Keepass2Android and <a href="https://github.com/noliran/ykpass">ykpass</a>.