The microKEY-61 AIR from Korg is a slim MIDI controller with a pitch wheel, a modulation wheel, and a set of 61 velocity-sensitive Natural Touch mini-keys. If you wish, you can bus-power this unit via the USB port, but the microKEY Air also features Bluetooth capabilities, allowing you to connect wirelessly to Mac and iOS devices. Hooked up in such a fashion, the keyboard can last up to 30 hours on two AA batteries (alkaline are recommended).
An assignable switch jack allows you to plug in a sustain pedal, while two octave-shift buttons allow you to change the range of this three-octave unit. You can make edits to MIDI parameters using the Korg KONTROL Editor software, which is available for free download on the Korg website. This can be useful in customizing the microKEY Air to your specific sensibilities, such as adapting the instrument's velocity curve to your individual touch.
The controller also includes five virtual instruments (Korg Legacy Collection, UVI Digital Synsations, AAS Ultra Analog Session, AAS Strum Session, and AAS Lounge Lizard Session), as well as two apps (Korg Module Le for iPhone and KORG Module Le for iPad). Finally, purchasing the Korg microKEY Air will allow you to download a limited version of Propellerhead's Reason.