Ecwid is a very popular choice.
Whether you are just a startup or looking to enhance your eCommerce business, Ecwid offers a FREE Plan. This is perfect for someone who is just starting out. You can always upgrade at any time you wish. Ecwid also offers an extensive app store, where you can choose from tons of useful apps to enhance your store.
Ecwide business plan comes with your own IOS/Android app. Not is it only simple to use, you can easily connect to your other sales channels.