Is TileMill opensource?

Question

I was reading this GIS.SE question about whether TileMill will be replaced by Mapbox Studio. I got worried about the future as a TileMill user, and the question suddenly came to me "isn't tilemill opensource?". Why can't we branch it if something goes wrong. To check, I went to their official website, and only found that [TileMill is]:

Powered by open source TileMill is built on a suite of open source libraries including Mapnik ...

Nothing is said about whether TileMill itself is open source. I went to the github site, and the license reads:

Copyright (c), MapBox All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. ...

The rest of the text looks pretty much open-source. What about the "MapBox All rights reserved." part? Does that conflict with the open-source spirit?

I am not familiar with the legal terms. But I don't see any familiar license terms like GPL, LGPL, apache or BSD.

My question is:

is TileMill open source or not?

Answer 1

TileMill is released under the BSD 3-clause license, an OSI approved license.

https://github.com/mapbox/tilemill/blob/master/LICENSE.md

So in answer to your question: Yes, TileMill is open source.

Mapbox Studio is released under similar terms:

https://github.com/mapbox/mapbox-studio/blob/mb-pages/LICENSE.md

Some more information:

• http://en.wikipedia.org/wiki/BSD_licenses
• http://opensource.org/licenses/BSD-3-Clause
• http://opensource.org/osd

This answer from the Mapbox Studio FAQ may also be of interest:

Do I need a Mapbox account to use Mapbox Studio?

Yes, a Mapbox account is needed to access the default vector tile sources included in Mapbox Studio. You can try out the features of Mapbox Studio for free but to make use of all of the functionality you must be on the Mapbox Standard plan.

You are not locked into using Studio with Mapbox – you can export vector tiles from any source project as a standard MBTiles file and package any style project as a .tm2z package.