Lockish

Lockish puts Touch ID in front of the apps you choose, like Messages, WhatsApp, your bank or your email, and leaves the rest of your Mac open. Lock them yourself with one click when you step away (everything at once, or one app), or let each app lock itself after you switch away from it, on a timer you set from 10 seconds to an hour; everything locks when the Mac sleeps or the screen locks. Only the protected app's windows are covered, so you keep working in everything else. One-time purchase, 7-day free trial, each licence on up to 3 of your own Macs. It's privacy on a shared Mac, not a vault: anyone with the Mac's password can unlock it. Made by Appish, a one-person studio in the UK.