Yes - Ruby Toolbox is handy, one of the discovery and currency assessment tools I use too, and is good at surfacing projects that are actively developed, but it takes a metric driven approach that's intrinsically weak at distinguishing between abandoned code and stable code, and has some occasionally peculiar/opinionated taxonomies that I’m not even sure are themselves adequately curated. It won't reveal when a decaying gem will cause other dependencies to be held back, and Ruby Toolbox suffers from the same fundamental blindness to compatibility with specific language edition that RubyGems has. Since it’s not a part of RubyGems, it ultimately can't offer a reliable barrier to inadvertently installing bitrotted code.

All that said & done, and to state this more constructively, I think there's a missing piece in the community infrastructure puzzle that someone could fill if they had the time, inclination, and build farm to do it.