Kobo Redux is an evolution of Kobo Deluxe, with smoother movement, a bit of physics, and various gameplay tweaks and updates, for a less frustrating experience.
The game is still in development, but the full engine source code is already available. The remaining work is mostly in the areas of graphics, sound, and music, and a substantial part of that is done already. A playable demo will be released as Region 1 (10 levels out of 50) is completed.
Kobo Redux will be released commercially, but the engine remains under the GPL, and comes with minimal themes, making it fully playable without proprietary data.
Kobo II [working title], though intended to appeal to Kobo Deluxe fans, is a modern, fast paced dual stick shooter. Physics, hardware accelerated high definition graphics, lots of weapons, new enemies, multiplayer etc.
The game is in development, but a playable Tech Preview has been released, and pre-purchase is open. See official site for further info.
Kobo Deluxe is an enhanced version of Akira Higuchi’s game XKobo for Un*x systems with X11. Kobo Deluxe adds sound, smoother animation, high resolution support, OpenGL acceleration (optional), an intuitive menu driven user interface, joystick support and other features. Recent versions also add a number of alternative skill levels with slightly modernized gameplay. Kobo Deluxe uses SDL for graphics, sound and input, which makes it possible to build and run the game on pretty much anything.
Kobo Deluxe is Free/Open Source software, and available free of charge!