There are ways to build a GUI using gems, or link excel and a ruby 
program in such a way that excel itself acts as your GUI.

I do a fair bit of work with both Excel VBA and Ruby, and the tool I 
choose depends on the task.

Generally, if the calculations are simple, and done direct from excel 
into excel, then VBA does the job.

If you have something complex that needs doing, then you can save 
yourself a lot of headache by writing it out in concise Ruby code.
This is ideal when you know the users have the framework installed, when 
you can use RoR, or when ".exe" builds are suitable.

One option is to use Ruby and Excel side-by-side, as each can trigger 
the other.

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