OpenBSD/armish runs on various ARM-based appliances, using the Redboot bootloader (and which boot Linux by default).
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OpenBSD/armish is the 3rd OpenBSD port to ARM based machines, after cats and zaurus. It is intended to support a variety of rather similar ARM-based machines:
Development is currently pretty active.
The latest supported OpenBSD/armish release is OpenBSD 5.4. Here are the OpenBSD/armish 5.4 installation instructions .
Snapshots are made available from time to time, in this location as well as in a few mirrors. Here are the OpenBSD/armish snapshot installation instructions as well.