The IOIO is a board that provides a host machine the capability of interfacing with external hardware over a variety of commonly used protocols. The original IOIO board has been specifically designed to work with Android devices. The newer IOIO-OTG ("on the go") boards work with both Android devices and PC's (details here). The IOIO board can be connected to its host over USB or Bluetooth, and provides a high-level Java API on the host side for using its I/O functions as if they were an integral part of the client.

All user documentation is on the Wiki.

You can get answers to questions and get news about IOIO on the ioio-users discussion group

The IOIO Gallery lists various IOIO projects to give you some ideas of what you can do with IOIO.

And this is the blog of Ytai, the inventor of IOIO, where new developments are normally announced. Specifically, this introductory post provides a good overview of this technology.

You can purchase a IOIO-OTG board online from:

• SeeedStudio (primary manufacturer - manufacturing, testing and service standards have been inspected).
• Sparkfun Electronics (primary manufacturer - manufacturing, testing and service standards have been inspected).
• Jaycon Systems.
• LinkSprite.
• CuteDigi.
• AliExpress.

in top build.gradle

allprojects {
	repositories {
		...
		maven { url 'https://jitpack.io' }
	}
}

and in module build.gradle

dependencies {
        implementation "com.github.ytai.ioio:IOIOLibAndroidBluetooth:$LATEST"
        implementation "com.github.ytai.ioio:IOIOLibAndroidAccessory:$LATEST"
        implementation "com.github.ytai.ioio:IOIOLibAndroidDevice:$LATEST"
}

Please see details here https://jitpack.io/#ytai/ioio