Projects that lived
An SDK for Amazon Web Services. Became the official AWS SDK for PHP in 2010.
A library for parsing RSS and Atom feeds in PHP. Became wildly popular and is now integrated into WordPress.
Projects that died
Blocked robots from visiting your website. Helped websites avoid referrer spam.
This was the project I was building SimplePie for in the first place. No code ever got written because SimplePie became so popular.