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If you are thinking about transitioning an organization to open source, pricing and vendor lock-in are generally good arguments.
If you are thinking about helping individuals transition, that's a bit more difficult. Pricing could still work, but is not always that effective. It boils down to the willingness to try something new.
In both cases projects with good documentation and a healthy community also helps, but if the open alternative lacks features, it's a though sell.
Thanks for the reply! I was thinking of a mixture of organizations and individuals, so both of what you mention is relevant.
Another perspective I'm interested in, and why I asked here, is for anyone around that may have helped organizations/individuals make the transition, whether through discussion and/or contributions to or tools for open software to better assist adoption.
The only such transition I was involved in was switching from TFS to Git, and there was no discussion. It was the obvious thing to do and for a while we needed to support some developers who are new to Git.
So, it all depends on the type of change you want to implement. Most people don't think much about a piece of software being open is significant. That's why the main selling point should be the product itself. Especially in organizations openness alone is not a strong enough argument.
But with individuals, it may help to inform people about FOSS instead of just suggesting alternatives ("Do you have a moment to talk about our lord and savior Stallman/Torvalds?"). If the individual doesn't understand or subscribe to the values, the switch may be temporary. My 2 cents. Hopefully others will come up with better tactics.
For programmers, WSL with Ubuntu is a good starting point for those who are scared of Linux.
That is definitely not a good starting point. WSL is much more complicated and prone to breakage than running a distro directly. It litteraly changes the whole system to make Windows run on top of a hypervisor. A better way to try out GNU/Linux is to boot up a live environment on a USB stick or use a VM. Plus, WSL is only command line, and I would think that showing a friendly desktop environment is the best way to blow the assumption of GNU/Linux being hard/only for nerds.
Points that can help them change to FOSS:
Sites that can help them find FOSS alternatives:
In my experience it's extremely hard to make someone not interested in software to try out new FOSS apps though..
You would be surprised with how common it is for the lay person to have problems on their computer. I like to start from there, and suggest a free as in freedom software solution. Then, once their issue has been solved, I will talk about the free software movement, explaning that these are the reasons that have motivated the authors of the software solution I promoted. Hopefully this leads on to a discussion about freedom in the digital world.
The software should speak for itself.
But it has to start speaking to them in the first place and I think OP was specifically looking for the "conversation starters"