How can I get a free POS software?

You can go to software recommendation platforms like SoftwareSuggest or Capterra. They provide personal consultation to your requirements and queries. Here you can check out the full list of the top POS Software, compare them with each other and also ask for free demo. 

download from the internet.
search and choose.

There are lots of POS programs developers who provide you a trial version depending the nature of your business.
Plus you can download free from the volunteer developers who simply provide it free for a limited period.
But always male sure that your POS machine configuration is compatible with the program you are adopting for its smooth functioning.

Hi you can download from the internet but as a demo vesion or trial software you can give the business category to give you some of companies you can download or buy from.

Hi, As mentioned in some of the posts above you can google and find several POS software vendors that provide free software, however, you must do due deligence to understand what the software can do for you and what it cannot and if your business requires a feature not available, then what would be the costs. 
Most software companies that provide such free software, end up milking their customers for various aspects such as: Installation and set up support Training support Single user to multi user / single terminal to multi terminal / single store to multi store support Add on module cost + installation and set up and training Consolidation cost + installation and set up and training etc etc etc ...
Initially what would seem economically viable suddenly bulges to be an expensive deal and will hit your profitability.
Good Luck!

Hi, I think that the best option it is to pay to some software developer for an ad-hoc tool adapted into your necesities However you can put "free pos software" in your search engine and choose the one that like you or the one that can adapt easily into your requirements.
It is important to check if the software it is compatible and easy to integrate into your data base.
Kind regards