List of free screenshots stuff for developerππ½
If you're looking for all programming tools around screenshots (not just free). Check this page List of screenshots Programming Tools

Puppeteer
Most things that you can do manually in the browser can be done using Puppeteer
Tag: screenshots, ui-testing, crawl

Refero - design references for your next project
The biggest collection of design references from great web applications
Tag: design, inspirations, web apps, screenshots
Free tier after sign up

ScreenshotOne
Fast and reliable screenshot API built to handle millions of screenshots a month.
Tag: screenshots
100 screenshots 20 requests per minute