Square Online Store is a new offering from Square. It's popular with cafes, restaurants, and other small businesses. It has a free plan where you incur a small % fee when you sell an item, or a paid plan.
Magento is an open-source platform for online shopping and inventory. It doesn't include product pages, blogs, or other marketing-type pages. Their basic offering is free, but you will need to pay an annual fee if you want to use this to its full extent.