Besides the popular Rails dictionary, here's a list of other dictionary files for Ruby libraries people ask me quite often:
Read more »Just released a new version of Rails 3.1 documentation for Dictionary.app together with rubydictionary gem. This gem is a RDoc formatter that turns any ruby documentation into a dictionary.
Let's keep it short this time. Rails 3.0 is out. Updated dictionary is out. Download it now and enjoy! If you don't know what this is all about, please read my previous posts. Read more »
This is a guest post by Siim Teller: And now for something completely different. Priit is too busy to blog himself this time and asked me to post instead. This is a deviation from his usual topics but don't change the channel, it's going to be interesting.
Rails 3 documentation is finally out for Mac OS X Dictionary.app. If you're not sure what this is about, please have a look at my previous posts on rather popular Ruby and Rails 2.3 dictionaries. Download your copy of Rails 3 Dictionary here. Read more »
YUI version 3 has been out for a while now, but still no dictionary? It took me some time to get myself together and spend couple of hours re-writing the scripts to build dictionary. Anyway, it's here now and ready for download. Enjoy! Read more »
YUI documentation inside Mac OS X dictionary gives you system-wide access to the docs - just about everywhere Dictionary.app is supported. For example Spotlight, Dictionary dashboard widget, "Look up in dictionary" context menu and almost any other Cocoa-based application if you dare to use Control+Command+D key combination. Read more »
With Rails 2.3 now out of the door, it was time to update the dictionary as well. Download Rails 2.3 dictionary for Mac OS X. Enjoy! Read more »
Shortly after publishing Ruby Dictionary, Mika Tuupola did the same with jQuery API documentation. He used jQuery documentation in XML format exported from wiki and some XSLT to boil things together which is a very elegant solution to do such things.
First version of Ruby on Rails dictionary had many glitches in it -- lot of the pages were blank and didn't show up on Spotlight search. These issues are fixed by now and dictionary file has been updated. So, download it right away while it's hot! Read more »

There are several great Ruby and Ruby on Rails API documentation browsing sites available on the web. But if you try to find that third argument for a method whose name you have forgotten from web it can really slow you down. So i finally took some time to generate Mac OS X dictionary out of Rails API docs which is ultra-fast and doesn't get in the way while you're coding. Read more »