1. UJS
Unostrubsive Javascript, write in web1.0 and render in Web2.0, Web3.0,.. This is an attempt to add behaviors to the MVC pattern. The power of the standards but also integrated effects.

2. Globalize
A smart way to add internationalization and globalization to your sites

3. REST
Provide datas corresponding to the request easly

4. RSpec
Add readable and easy to mantain tests to your code

5. Rjs
Write the code in ruby also for the client-side

6. Capistrano
Develop locally and put the working code easly in production

7. Webserver indipendent
Apache, lighttpd, mongrel,.. Choose the webserver with the performance, features you need

8. Database indipendent
SQlite, Mysql, Postgresql, Firebird,.. You can choose the backend technology you prefere (as above)

9. Free Text editors / IDE with plugins, snippets, syntax highlight, autocompletion,..
Gedit textmate-like, Eclipse RDT/Aptana, Ride-me

10. Community
Documentation, Screencasts, Forums(1,2,3)