I’ve been using Ruby/Tk some time. It is quite good GUI toolkit, however very poorly documented. Well there is a lot documentation, but it is hard to start writing Ruby/Tk applications, since documentation is meant for advanced users. And how to become one?
Well it may change in future. First, there was new Tcl/Tk release (8.5) and this may put some new life into Tk world. This release is first from long time, and brings a lot new features to build modern GUI. Currently Tk 8.5 is not ported to Ruby, but I hope it will change in future.
And as for Tk’s documentation for newcomers – I’ve recently discovered site TkDocs which author promises try to make Tk documentation more user friendly. There is also group devoted to Ruby/Tk toolkit on Google.
You can keep an eye how work over new docs site is going on TkDocs blog.
At time like this, its sometimes a good idea to take a look at the corresponding Perl module’s documentation. There’s a lot out there on Perl/Tk, and since the ruby API is most likey based on the Perl version, the info should help you out.