Ruby is copyrighted free software by Yukihiro Matsumoto <matz@netlab.jp>.

As of Ruby 1.9.3, the Ruby Language went from a Dual GPL/Ruby license to Dual BSD/Ruby license. The intent of the icalendar license is that it is provided under the same terms as Ruby itself. The way we’re going to interpret this is the software can be redistributed under any of the 3 licenses, GPL, BSD, or the conditions below, at your option:

1. You may make and give away verbatim copies of the source form of the
   software without restriction, provided that you duplicate all of the
   original copyright notices and associated disclaimers.

2. You may modify your copy of the software in any way, provided that
   you do at least ONE of the following:

     a) place your modifications in the Public Domain or otherwise
        make them Freely Available, such as by posting said
        modifications to Usenet or an equivalent medium, or by allowing
        the author to include your modifications in the software.

     b) use the modified software only within your corporation or
        organization.

     c) give non-standard binaries non-standard names, with
        instructions on where to get the original software distribution.

     d) make other distribution arrangements with the author.

3. You may distribute the software in object code or binary form,
   provided that you do at least ONE of the following:

     a) distribute the binaries and library files of the software,
        together with instructions (in the manual page or equivalent)
        on where to get the original distribution.

     b) accompany the distribution with the machine-readable source of
        the software.

     c) give non-standard binaries non-standard names, with
        instructions on where to get the original software distribution.

     d) make other distribution arrangements with the author.

4. You may modify and include the part of the software into any other
   software (possibly commercial).  But some files in the distribution
   are not written by the author, so that they are not under these terms.

   For the list of those files and their copying conditions, see the
   file LEGAL.

5. The scripts and library files supplied as input to or produced as
   output from the software do not automatically fall under the
   copyright of the software, but belong to whomever generated them,
   and may be sold commercially, and may be aggregated with this
   software.

6. THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
   IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   PURPOSE.