Natalie Gaber let us know that the Sierra Club launched a new website Thursday, July 9th.
It’s called Sierra Club Trails, the first hiking wiki. (So far as we know.)
Using Wetpaint software, anyone can edit any of their listed trails. For example, check Angel’s Landing in Zion National Park. (You can read that page. But must log-in to edit.)
Or start from the home page:
I’ll be researching it in detail. I’ve long wanted to convert our list of the best hikes in the world into a wiki.
besthike.com 
Portlandhikers.org have a trail wiki. It’s one of my favorite hiking websites. It doesn’t look as shiny and polished the the Sierra Club site, but it’s very user friendly.
http://www.portlandhikersfieldguide.org/wiki/Main_Page