The incumbent is rarely bad — it’s just heavy. Finder makes you click down a tree, Preview takes its time, Photoshop wants a subscription before it will give you a layer-styles panel, and reading a Markdown file means opening something first. Each of these is the small, fast, native answer to precisely one of those complaints.
A native Mac file manager built around fuzzy-find
→ whimfiles.com
A lightweight Mac paint app with real Photoshop-style layer styles
→ mojavepaint.app
Real Markdown previews — Mermaid, math, syntax highlighting — from the Finder spacebar
→ markedapp.com