Update: 6:45 p.m. GMT, As far as I know, you can just install the binary package of RubyCocoa and the default Apple installation of Ruby will be sufficient to make this app work.
Update: 6:19 p.m. GMT, I fixed a bug in the checker. Get the new one as usual from the Box widget.
Application icon credits: rox-ruby
I have uploaded a little Regular Expression checker I made in RubyCocoa(see RegEx.dmg in my Box widget to your left). I only have an Intel Mac to test it on, so I have no idea whether it will run correctly on PPC Macs. The code is licensed under the GPLv2. It may be the case the that you need RubyCocoa properly installed to run this app. See my post on installing BioRuby for Mac OS X for a link to Dan Benjamin’s instructions on updating your Ruby installation(adapt these instructions accordingly for Ruby 1.8.5). For installing RubyCocoa under Ruby 1.8.5, if memory serves, these commands (once you extract the files from the archive and go to the to-level directory of RubyCocoa),
$ ruby install.rb –help # print all options
$ ruby install.rb config
$ ruby install.rb setup
from this website are the key instructions. You may have to prefix sudo in one of the above three commands.
NO WARRANTY 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.