kazaam wrote:
> require 'rubygems'
> gem 'wxruby2-preview' 
>  
> 
>  class MinimalApp < App

the error is here.

> ./gui.rb:9: uninitialized constant App (NameError)
> laptop:~/Desktop$ 

You have chopped out a bit too much from the sample you copied. The 
class you want to inherit from is Wx::App, so you need to either 
reference it fully:

  class MinimalApp < Wx::App

or, include the whole Wx module in your main namespace at the beginning 
of your script (as in the sample you started from):

  include Wx

Then you don't have to add the Wx:: prefix whenever you reference a 
wxRuby class or other constant. The choice is yours; "include" saves a 
bit of typing in short scripts, but it's probably clearer to use the 
Wx:: prefix in bigger applications.

> ruby: 1.8.5 (2006-08-25) [i486-linux]
> wxruby2-preview: 0.0.40 .

Not relevant to your error, but I'd recommend upgrading to wxruby-1.9.0, 
which is a newer, beta-quality release off the wxruby2-preview series.

alex