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"You get what you pay for." It's an old saying, one that typically means that if something is free, then it probably isn't worth much.

But in the world of technology, the exact opposite is often the case. Over the last 20 years many of the most innovative and useful products and technologies that we've seen are those that users and businesses could take advantage of for no upfront cost whatsoever.

And while there are some people out there who disparage free and open-source products and technologies as being copycats of commercial products (not that those don't exist), in many cases it is the free and open-source products that are breaking new ground and setting the course for other free and commercial products to follow.

With that in mind, I've put together this list of 20 free products and technologies that proved to be innovative and that ended up changing the future of technology. Some were open source, some were freeware, and some started out free, flirted with commercial models and then returned to free status. But in all cases, users of these technologies got quite a bit of value from them. In fact, they got quite a bit more than what they paid for, even if they had paid a lot more than nothing.

So take a look at my list of the Most Innovative Free Technologies, and comment below to let me know what technologies and products would make your list.