Great article 
Also worth mentioning:
- the_metal (rack 2.0 ideas by tenderlove)
- Lotus (new Ruby webframework) http://lotusrb.org
- trailblazer (new architecture on top of rails) https://github.com/apotonick/trailblazer
- rubinius 3.0
Sorry can only put 2 links in a post (new user restriction)