In late 2009, I was introduced to Obsidian Portal as a website destination for planning, organizing, and progressing RPGs. Deciding to delve into it, I started to do my world building for the Hackmaster Basic game I run monthly. Wow! I really enjoy using this tool quite a bit and would highly recommend it to other GMs.
Some of the things I really like:
* Private GM only notes on all pages and character sheets and GM exclusive pages
* The way the Adventure Log is not in a wiki format, but a blog format
* Wiki-style organizing!
Something I wish they did:
* Have more interactive database-type options for the character sheets
Here is the link to my campaign:http://www.obsidianportal.com/campaigns/hackmaster-glyndael-chronicles