* Cryptocurrencies who's sole reason to exist is to justify its own existence. "We need token X to perform operation Y. Operation Y is important to facilitate the trade of token X". Seriously, how many tokens exist for the only purpose of being "gas" for its own network?
* Social networks that only discuss itself and its own existence.
* Programming languages where the largest project written in that language is its own compiler.
Solutions in search of a problem, is what they are.