> It is not listed in the Linux Mint App Installer. The Portables downloaded from Sourcefoge do not work.

It's packaged in Debian and Ubuntu as "doublecmd-qt" and "doublecmd-gtk", so Linux Mint ought to have it as well.

> Can it filter-as-you-type the file list?

Yes.

> Does it have chainable script button bars?

I don't know what that is.

> Is there a poweful rename tool?

There's a Multi-Rename Tool, yes.

> Can it look pretty

You'll have to be the judge of that. It looks good to me. It uses the Lazarus component library, so it can be built with either Qt or GTK (or native win32 on Windows) and uses whatever themes and configuration applies to those.