Afloat might be a bit more popular than Duplicate Windows. We know about 1 link to it since March 2021 and only 1 link to Duplicate Windows. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
I haven't used this personally, but it may get you some of the way there: Duplicate Windows app. Source: about 1 year ago
You can try Afloat (useafloat.com) and see if it works for you. It focuses on simplicity and ease of use. Disclaimer: I'm the founder and developer. Afloat is developed from Malmö :-). Source: about 2 years ago
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Pennywise - Cross-platform application to open any website or media in a floating window
PiP-Tool - PiP tool is a software to use the Picture in Picture mode on Windows.
PiPer - A DIY Minecraft computer to build gadgets
Picture In Picture - Picture In Picture comes as an extension tool that enables users to watch videos in a floating window.
Free-Invoice.co.za - Free Invoice Software | Free online tool that helps small businesses to generate free invoices and manage their contact list. It can be used as an alternative to expensive invoicing software and online invoicing applications