[Foivos]

One of the reasons for this popularity is the permissive license. I would guess that the license is MIT, but seems to be a bit different [1]. Does anybody know (in simple words) what are the main differences with MIT? The copyright webpage does not elaborate.

[1] https://curl.se/docs/copyright.html

[nicoburns]

The following seems to be the major addition compared to the MIT license:

"Except as contained in this notice, the name of a copyright holder shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization of the copyright holder."

[F3nd0]

There doesn't seem to be a single canonical MIT licence, but rather several co-existing variants of it. The part you quote is a standard part of the X11 variant [1], while the Expat variant does not include it.

[1] https://www.gnu.org/licenses/license-list.html#X11License

[tempay]

The SPDX license identifiers are the best thing we have for defining what the canonical version is (which is used by expat): https://spdx.org/licenses/MIT.html

There are many MIT-derrived licenses, some of which have identifiers prefixed with MIT- and others like X11 and curl have independent identifiers: https://spdx.org/licenses/

[F3nd0]

All the more reason to avoid calling any one licence ‘the MIT licence’, in my opinion. While I appreciate that SPDX provides a comprehensive list unambiguous identifiers, I don’t really see why they would be best suited to determine which of the many variants a name has been used for is the best candidate.

That’s not to say they necessarily aren’t; I’d be interested to see if any rationale behind that choice has been published anywhere. But if the choice was made more or less arbitrarily, or based on what seemed more popular to the authors, I’d be inclined not to treat SPDX as an authority on the matter.

[justin66]

The existence of the advertising clause was always the main difference between the traditional BSD license and MIT license. The above is interesting because it's also an an advertising clause, but it does something the opposite of what the BSD advertising clause did. BSD wanted the license and the Regents to be mentioned in advertising.

[F3nd0]

It appears to be a custom licence, which, as stated on the page, is inspired by the MIT/X11 licence. The only difference from MIT/X11 appears to be the the part before the warranty disclaimer, which has been shortened. SPDX has a separate entry for it [1].

[1] https://spdx.org/licenses/curl.html

[nhubbard]

It's like a combo between the MIT license with the 3rd clause from the BSD 3-Clause license.