I have just installed Sequel using the command
sudo macgem install sequel
/Users/.../macRuby Test/Tests/run_suite.rb:1:in `<main>': super: no superclass method `require' for Sequel:Class (NoMethodError)
SIGABRT in MacRuby 0.7 with Sequel + SQLite3-Ruby gem
[...] After patching for Kernel#require issue in Sequel, I am able to load both Sequel, and SQLite3, with no problems. [...] Required libraries are Sequel (Patched for Kernel.require, instead of super in Sequel#self.require), and SQLite3-Ruby. [...]
What version of MacRuby do you run? Also, do you run a 32-bit Mac?
In my environment, 64-bit Intel mac running MacRuby trunk, I am able to install and require sequel.
$ /usr/local/bin/macruby -r rubygems -e "require 'sequel'; p 42" 42
As Eloy said, it is better to report MacRuby problems to our mailing-list or ticket trac instead. http://www.macruby.org/contact-us.html