The free HIV vaccine.
Immunity Project was funded by Y Combinator on 2014-01-01 at immunityproject.org. The site still answers.
Across the whole register, 23% of launches whose fate we could settle are gone.
How we know. Show HN and Product Hunt entries are judged by asking the domain whether it still answers: gone means it no longer resolves, refuses the connection, serves a parking page, or says plainly that it has shut down. An HTTP error is not counted as gone — a server that answers 404 is one somebody still pays for. Y Combinator entries use the status YC itself publishes, which is why only those can say acquired. Search the whole register.