First of all, MEAN is an acronym for MongoDB, Express, Angular and Node.js.
It generically identifies the combined used of these technologies in a "stack". There is no such a thing as "The MEAN framework".
Lior Kesos at Linnovate took advantage of this confusion. He bought the domain MEAN.io and put some code at https://github.com/linnovate/mean
They luckily received a lot of publicity, and theree are more and more articles and video about MEAN. When you Google "mean framework", mean.io is the first in the list.
Unfortunately the code at https://github.com/linnovate/mean seems poorly engineered.
In February I fell in the trap myself. The site mean.io had a catchy design and the Github repo had 1000+ stars. The idea of questioning the quality did not even pass through my mind. I started experimenting with it but it did not take too long to stumble upon things that were not working, and puzzling pieces of code.
The commit history was also pretty concerning. They re-engineered the code and directory structure multiple times, and merging the new changes is too time consuming.
The nice things about both mean.io and mean.js code is that they come with Bootstrap integration. They also come with Facebook, Github, Linkedin etc authentication through PassportJs and an example of a model (Article) on the backend on MongoDB that sync with the frontend model with AngularJS.
According to Linnovate's website:
Linnovate is the leading Open Source company in Israel, with the most experienced team in the country, dedicated to the creation of high-end open source solutions. Linnovate is the only company in Israel which gives an A-Z services for enterprises for building and maintaining their next web project.
From the website it looks like that their core skill set is Drupal (a PHP content management system) and only lately they started using Node.js and AngularJS.
Lately I was reading the Mean.js Blog and things became clearer. My understanding is that the main Javascript developer (Amos Haviv) left Linnovate to work on Mean.js leaving MEAN.io project with people that are novice Node.js developers that are slowing understanding how things are supposed to work.
In the future things may change but for now I would avoid to use mean.io. If you are looking for a boilerplate for a quickstart Mean.js seems a better option than mean.io.