We have removed Product Groups from the core Spree project. This was a rarely used feature; but, the code was fairly complex. In an effort to keep Spree lean, the code was extracted and moved to an extension.
The commit to Spree Master will be part of the 1.1 release. If you are using Product Group functionality, then you’ll want to include the extension in your Gemfile after ‘spree’.
It has not been released as a gem, so you’ll have to declare it with a reference to the git repository.
All previous Product Group functionality will be restored by the extension.