Debian is is linux distro, you can download sofware for several types of PC, and other platforms from debian.org, and run it on your PC or virtual machine, etc.
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BeagleBone is as single board computer that can run linux.
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. open-source hardware.
Raspberry Pi is the same sort of thing. (but not open source hardware)
All of the above can also run some version of BSD which is not just unix like but actually Unix.