[ac2u]

You'll probably not get many answers here because the list of what you're looking for is so long with a quick Google for "open source pos systems".

What you'll learn when you get into this is:

1) Accepting credit card payments is a service which needs a cut of that transaction to exist and be a functional financial network, so looking for open source software can't eliminate that cost in isolation.

2) There's a reason small businesses still find it worthwhile to pay for a POS system (usually with a monthly service payment). Because self hosting can often be beyond the expertise of the user, and even if it's within their expertise, they might decide their time applied elsewhere is more lucrative. What I'd imagine you'd find is that some businesses may choose to gravitate towards the free and open solutions not because they lack money, but because their needs are complex and niche and it's worthwhile for them to spend time and money customising and hosting.