It was here a "minute ago" - https://github.com/magento/magento2-samples and now it's not there for more than a day. I did not see any announcement that samples will go somewhere. Docs still link to this repository.
Go to Solution.
The link is changed:
That just links to the sample data, the sample modules were different. Magento have removed them as they're now out of date.
Source - https://github.com/magento/devdocs/issues/1133