I am working on popularizing Apache Solr search engine: http://www.solr-start.com/ . It's a couple of books, a website, a mailing list and a bunch of connected Open Source projects, all having the focus on making it easier for people to learn Solr.

The fun part is that doing this for/by myself, I can scratch any itch I want, as long as it's around the core theme. The extra interesting - and challenging - part is to ensure there is a positive-feedback and self-fulfilling prophecy across those products.