What's the "experiment"? The FAA system, I suppose - apparently not followed elsewhere.
Not quite so, the Australian and NZ systems are similar, in Australia Experimental Amateur Built is one of the several categories within Part 21, Experimental.
Again, in Australia the current legislation superseded the AABA -- Australian Amateur Built Aircraft system, which was highly bureaucratic and restrictive.
Many of the Experiment Amateur Built aircraft are highly customized, from basic designs, many are unique designs, but they all have one thing in common, they do not qualify for a Certificate of Airworthiness. Indeed, by definition, they are not airworthy, because they are not built to a certified design and under a production certificate.
Tootle pip!!