You drop in a screenshot, choose a browser, phone or laptop scene, adjust the layout and export an image for your landing page or launch post. There are 3D device scenes too, and a fuller editor for arranging multiple mockups, text and backgrounds.
Editing and export happen in your browser, and designs are saved locally. Your images only get uploaded if you explicitly enable the optional Pro cloud sync.
The free version needs no account and includes all current frames and editing tools, with unlimited individual PNG/JPEG exports and no watermark. Pro adds things like batch exports, transparent backgrounds and cloud sync.
It's built for desktop browsers. You can try the example linked above or see more at https://usebrayer.com.
I'd be interested to hear what you use for your own product screenshots, and where Brayer falls short for that workflow.