Someone pins the "recipe" for their software on the wall with a note: copy it, change it, even open a shop and sell it. Just don't tear off my name, and if anything goes wrong, don't come to me.
A "license" is that note stuck next to the recipe: what the owner lets you do with it, and what they don't. MIT is the loosest and most common kind.
2
How it differs from what you'd expect
NO NOTE AT ALL
You can look, but not take
Being on public display doesn't mean it's a gift. With no note, it still belongs to the author alone.
A "GIVE IT BACK" NOTE
You can take it, but your changes must be shared too
If you use my recipe, your new recipe has to go on the wall too, for everyone to copy.
THE MIT NOTE
Take it, change it, keep your changes private
The only ask: keep the original author's few lines.
In plain words: MIT is "almost free", and all it wants is credit.
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The whole note says three things
① Use it freelyUse it, copy it, change it, build it into your own thing, sell it on. All fine
② Keep the nameThe author's credit and this note have to travel with the thing
③ No refundsWhether it works is up to you. If it breaks or costs you money, the author is not responsible
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It's all around you
The sites you browseMany websites are built from parts taken under this very note
Apps on your phoneThat long "open-source notices" page in Settings is rows and rows of preserved credits
Software companies sellTaking it, tweaking it and putting it in a paid product is perfectly allowed
Why so popularShort, about 170 words anyone can read; loose, so nobody worries about stepping on a trap
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One thing it won't give you
No warrantyIt's handed over "as is". If it breaks or costs you money, the author pays nothing. So test what you take, and be your own safety net.
"Can I build a product from someone's MIT-licensed work and sell it?"
Yes. The author allowed exactly that. Just keep their note, unchanged, inside your product. And the other way around: put MIT on your own work and you're telling the world, take it, just remember me.
