There are many good web frameworks out there which can be used to create custom web services/sites. Mewlo is not an entirely new kind of thing; Django
is probably closest in scope (at least in Python).
A main thing that makes Mewlo different is that it is focused on user-account-centric sites and will support such things in its core: User accounts, rich user profiles, cross-site logins, user groups and projects, user messaging, forums, tagging, rating, etc.
It's not that you can't create such functionality by coding it yourself once you start with these other frameworks, or by cobbling together dozens of semi-supported addons -- but Mewlo is an attempt to create a cutting-edge and tightly-integrated framework for this stuff, and for the backend administration of it.
So for example, if you wanted to create a user-centric site like boardgamegeek, deviantart, facebook, etc. You could build it on top of any of these existing frameworks like Django, Drupal, etc. But you would have to write a huge amount of additional code to support the user and group account features, and you'd probably be installing dozens of addon extensions that you might have difficulty getting to cooperate -- and then struggling to keep all of these disparate components maintained.
The goal with Mewlo is to create a framework that provides more core infrastructure support for, and a more cohesive vision for creating these kinds of large complicated sites where users are the focus.
When a web framework like Django or Drupal provides support for something like user profiles, they do so as an effort to provide a fairly bare bones implementation, that makes few assumptions about the features and functionality that will be needed for such things. This is a deliberate decision to be agnostic about how user profiles should be supported and what features will be needed, and makes sense given the fact that many developers will be using Django/Drupal to build sites that do not make use of rich user profiles.
The drawback is that whenever any developer does want to provide the kind of modern rich user profiles (and groups, and user messaging, forum, etc.), they must reinvent the wheel, or struggle to combine and maintain a large collection of third-party addons which rarely work well together for long.
With Mewlo, the goal is to provide support for best-in-class implementation of the kind of features you find in a modern user-centric web service -- with components that are stable, tightly integrated and maintained, to provide a predictable cohesive foundation for a developer.
Mewlo is firmly in the camp of "there is one right way of doing things" than some of these other frameworks, and will sacrifice some flexibility in favor of increased clarity-of-vision, uniformity, predictability, stability, etc.
A good tagline for Mewlo would be: "No more reinventing the wheel."
I've written quite a bit about Mewlo, it but it's on a private document that I need to make public. I will try to do so soon.
As I said, it's a very big project, and I'd love to have some partners working on it with me (as well as line up some sponsors for it).