I've been selling online since 1998. And in all of those years, I've tried and tested an insane number of tools, desktop software and apps and online services, as you can probably imagine. And today, it's just absolutely crazy to think that I depend on so many of these tools on a day-to-day basis, yet I've never had to pay for most of them. All of these are either completely free, and/or open source, or offer a free tier that I can pay to get additional features - basically a freemium (free + premium) service.
So here are some of the greatest free and freemium tools most of which I couldn't - and wouldn't want to - live without.