YARD is a documentation generation tool for the Ruby programming language. It is a very powerful alternative to RDoc, actively developed and maintained by Loren Segal.
YARD allows you to use Markdown or Textile to write your documentation, provides structured tags to better describe your methods and has a very advanced parsing mechanism. It is also under active development, which is a very good sign of interest.
Back in September I asked for feedback about using YARD over RDoc and YARD won with full consensus.
I'm now proud to say that the master branch of the Whois library is now entirely documented with YARD. It took several weeks, but I'm really satisfied with the result. I also had the chance to fix several documentation errors and increase documentation coverage.
The YARD documentation will eventually replace the current Whois RDoc documentation. I'm sure that it will be an awesome integration to the existing Whois manual.
In the meantime, you can try it yourself by downloading the library from GitHub and using the YARD server, another awesome YARD feature.
$ gem install yard
$ git clone https://github.com/weppos/whois.git
$ cd whois
$ yard server --reload
I already converted the Public Suffix Service API documentation to YARD a few weeks ago.