I was prompted by a discussion on LinkedIn regarding the use of Open Source e-commerce software - as opposed to licensed Software. Screen Pages we used to design/build clients on Licensed Software and now we do so on Open Source.
We don't believe in creating our own proprietary platform - I did this in my last business and the R&D & maintenance costs are enormous (you need a deep balance sheet to fund this as well as being reliant on a few ace developers).
So we like using other people's platforms. We started using Magento (Open Source) and it's incredibly feature rich plus has literally thousands of extensions. It's fully customisable, so you can design/layout as befits the brands we work with. The company behind it is quite well structured in terms of releases, but we offer all the support the client needs as well as ongoing updates. We have over 20 Magento clients now.
It's not without issues - especially in the realm of configuration & manageability for larger, distributed systems (how we run things). It's more to learn for clients as there are many configuration tools and options. That said, our costs have come down and by extension, the fees to the client for creating like-for-like websites.
Plus - and this is the game-changer - clients can take it with them rather than be locked in to proprietary platforms. We've taken on several existing Magento sites where the client wanted "different service" (shall we say) or the previous provider was no longer popular.
Having been a license man all my life, I am happy with our open source investment.