OpenBravo POS used to be ok, it even worked with barcode readers. But you could also manually punch up a sales receipt and it would adjust on hand numbers automatically. But Open Bravo has moved on to a cloud paid model. However there a few forks from the before time, like Unicenta, but I've never used that one and can only vouch for what it was back in the day. Source: almost 3 years ago

I would recommend going with https://opensourcepos.org/ or https://unicenta.com/. Source: almost 3 years ago

Unicenta works pretty well on a POS that I salvaged from a shop closure last year (no reason for doing so - just thought it would be cool to have one for the hell of it). Runs on Linux as well as Windows if you want to escape Windows Embedded 7. Source: almost 3 years ago

Looks like Unicenta is an alternative POS that can be self-hosted and is licensed as GPL-3.0-or-later. Source: about 3 years ago

However, I cannot open the HTML returned for the webpage https://okapiframework.org/ because there are certain unrecognized characters that appear with a question mark symbol. Python returns an error when I try to open the file:. Source: about 3 years ago