Flashboot is a system built by Damien Miller and others as an adaptation of OpenBSD that's more suited for small flash-based hardware. For most applications you don't have to compile it on you own, you just put the binary release on a flashcard and you're set (somewhat simplified).
All kernels and images are gzipped. However the OpenBSD bootloader and Physdiskwrite support gzipped kernels and images, so there is no need to unpack them before use. However if you use dd to write an image to the flash you will need to extract the image with gunzip first (ex. gunzip -c image.gz | dd of=/dev/sd0c).
IMPORTANT!! If you are upgrading using only the kernel-version from a version earlier to 4.4 you will need to update the bootloader. Failure to follow this advice will render your device useless. You have been warned! ;)
Kernels can be uploaded to an existing system, just replace the old bsd with the new kernel and reboot. Images are for brand new flash-cards that needs the bootloader and filesystem. These images are adapted for use with a 128 MB flashcard. If you use a larger card you will loose the remaining diskspace.
Please read the README before using these kernels and images!
Flashboot is now hosted on Github and can be downloaded here https://github.com/openbsd/flashboot.
Binary images can be downloaded here https://github.com/openbsd/flashboot/downloads