Retro gaming fans, rejoice, as the iCADE Software Development Kit is now free – in other words, developers willing to make their game compatible with the arcade cabinet will now be able to do it without having to pay a fee to its manufacturer, ION Audio. If you never heard about the iCADE, this iPad-compatible arcade cabinet started as a joke, and was announced by ThinkGeek on April Fools’ Day last year. The concept received such a warm reception that the company finally decided to turn the idea into a real product. After a few brainstorming sessions, ThinkGeek ironed out the device’s specifications, and partnered with ION and Atari to bring the iCADE to the masses. The iCADE is very straightforward, and to use it, users simply need to slide their iPads into the cabinet’s cradle. The iCADE actually uses Bluetooth to connect to the iPad, so no need to worry about messy connections between the cabinet and the tablet. Atari, the old school arcade games company, already made its greatest hits collection compatible with the device, with games like Asteroids, and many others. Now that the device’s API to allow third party developers to add iCADE support to their games is free, a slew of new iCADE-compatible games should hit store shelves very soon. The cabinet offers a joystick, as well as 8 action buttons, more than enough for most classic games out there. The iCADE costs $99.99.