Unindexed is an online community that anyone can contribute to; it runs a back-end process that continuously scours Google for signs that it has been indexed, and securely erases itself once it discovers evidence of same.
It's a cute art project (as opposed to a cute engineering project, which would have just used a robots.txt file to stop Google from indexing it altogether), and apparently included some kind of artistic statement of purpose that was nuked, along with the rest of the site, when Google indexed it 22 days in.
Nothing has been done to prevent the site from being indexed, however the NOARCHIVE meta tag is specified which prevents the Googles from caching their own copy of the content.
The content for this site is stored in memory only (via Redis) and is loaded in via a file from an encrypted partition on my personal laptop. This partition is then destroyed immediately after launching the site. Redis backups are disabled. The content is flushed from memory once the site detects that it has been indexed.
The URL of the site can be algorithmically generated and is configured via environment variable, so this source code can be made public without disclosing the location of the site to bots.
Visitors can leave comments on the site while it is active. These comments are similarly flushed along with the rest of the content upon index event, making them equally ephemeral.