Screenshot Machine - Screenshot machine is an online website capturing service. Creates a screenshot or thumbnail of any online web page in couple of seconds for free.
ShareX - ShareX is a free and open source program that lets you capture or record any area of your screen...
URL2PNG - Screenshots as a Service. Capture snapshots of any website, right in your app, quickly and reliably.
Thum.io - A real-time website screenshot generator
ApiFlash - ApiFlash is a powerful serverless screenshot API built with Chromium and AWS Lambda. It can easily scale to millions of screenshots per day and has an ever growing number of satisfied big clients.
ScreenTray - A better way to capture, annotate and share screenshots