Pennywise

Pennywise opens a website or media file in a small window that stays on top of every other app. You can resize and move the window, change its opacity, and switch to a detached mode where clicks pass through to the window underneath. For video sites such as YouTube and Vimeo it can show only the player, without the rest of the page. It suits anyone who watches or follows something while working in another app.

The README says the project is not maintained and points to the author's other app, Always on Top. The latest release, 0.8.0, is from 2019, although the repository has commits up to December 2025. The README lists macOS, Windows and Linux, and says the opacity shortcuts work on Windows and macOS only.