I've got some rough metadata tooling in the FuseIT SFDC Explorer (Disclaimer: A free tool distributed via my current employer). It's windows only at this stage.
I say rough because this particular area isn't at all refined or intuitive. Building it out stalled in favor of other areas that Workbench didn't already support.
From the Metadata Retrieve tab you can select the Metadata type of interest. E.g. ApexClass. Then press the "Get Package Component Type" button and it will dump out all the component names of that type.
Let me know if this sort of thing appeals and I could put some effort into it to make it more useful.
Update: So, umm, this particular feature is broken in the current public release. I'll try and get a release out for it soon. I'm aware of the irony considering the current situation with Workbench :)
You might also have some luck with the Salesforce DX CLI. You can use it to retrieve the package metadata. You might need to create a custom extension based on jsForce to get fine grained access to the component names.