TL;DR: Mapbox Studio classic is not as good as Tilemill, Mapbox studio is very promising, but you still need to signup for access, and kosmtik seems to be working right now. Use kosmtik and help getting it in Debian.
I have been following the development of fascinating tools from the Development seed people, now seemingly all focused on the Mapbox brand. They created what seemed to me a revolutionary desktop tool called Tilemill. Tilemill allowed you to create custom map stylesheets on your desktop to outline specific areas or patterns or "things". My interest was to create outdoor maps - OSM has pretty good biking maps, but no generic outdoor tiles out there (I need stuff for skiing, canoeing, biking)...
Mapbox has Mapbox outdoors but that's a paid plan as well. Oh and there's a place to download Garmin data files especially made for outdoors as well, and that could be loaded in Qmapshack, but they don't have coverage in Canada at all. Besides, I would like to print maps, I know, crazy...
So I have been looking forward to seeing Tilemill packaged in Debian given how annoying it is to maintain Node apps (period). Unfortunately, by the time Debian people figured out all the Node dependencies, the Tilemill project stopped and has been stalled since 2012. It seems the Mapbox people have now been working on other products, and in the meantime, the community, scratching their heads, just switched to other projects.
Overview of alternatives
So Here's a summary of what happened so far, after Tilemill development stopped. Hang on to your tiles boys and girls, there's a lot going on!
Mapbox Studio classic
Mapbox people have released a new product in September 2014 named Mapbox studio classic. The code is still freely available and seems to be a fork of tilemill. Mapbox classic still has releases on github, last one is from November 2015. It looks like Mapbox studio classic has some sort of Mapbox.com lock-in, and there are certainly new copyright issues, if only with the bundled fonts, but it could probably be packaged after addressing those issues.
There is an ITP for Mapbox Studio classic as well.
Then there's Mapbox Studio, which is a full rewrite of Mapbox Studio classic. You need to "signup" somehow to get access, even though parts of the code are free, namely the Mapbox GL studio project. It is an interesting project because it aims to make all this stuff happen in a web browser, which means it "should" work everywhere. Unfortunately for us, it means it doesn't work anywhere without a signup form, so that's out for me at least.
That is actually the ITP for Mapbox studio classic.
The Openstreetmap-carto developers have mostly switched to kosmtik instead of Mapbox. Kosmtik is another Node desktop app that seems fairly lightweight and mostly based on plugins. Ross has an ITP for kosmtik. The package is waiting on other node dependencies to be uploaded (yes, again).
The future of Tilemill
And there's still this RFP for tilemill, which should probably be closed now because the project seems dead and plenty of alternatives exist. I wonder if node some dependencies that were packaged for Tilemill actually now need to be removed from Debian, because they have become useless leaf packages... I am leaving the Tilemill RFP open for someone to clean that up.
Oh, and finally one could mention another Mapbox project, Carto, a command line CSS tools that implements some sort of standard CSS language that all those tools end up using to talk to Mapnik, more or less. There are no RFPs for that.