I always build with gb. I am not sure if I've made this thing goinstall-friendly. If you run into trouble with goinstall, please let me know!
This library is still very experimental. It is a replacement of the former gui library that I (David Roundy) worked on.
The gui package exports almost everything you should need to create a gui program, with the single exception being the lack of a function to make your gui actually run. That is provided by a "back end" package. Currently there is just one back end, gui/web, which provides a web interface. I hope that eventually, further back ends will be provided, possibly as third-party packages.
There aren't many widgets yet. Widget-creation comes in one of two varieties. A composite widget can be created in a package that only imports from gui itself. However, if you want to create a new primitive widget type (e.g. a color map or file selector), you'll need to create a new type in gui/data, and add support for it in gui/web (and any other back ends that are developed).
The API is based around chans and interfaces, and hopefully is a nice go-like API.