Thanks for letting us know, it looks indeed VERY interesting! While it works, I would say it is in quite an early stage of development, but is definitely moving in the right direction. Something like this was long overdo so it is good to see someone finally doing this.

A couple of my initial observations:

• based on the videos and the demo on the website the performance looks very good !
• it looks like it uses vector tiles and does some caching of them locally
• it seems to do only basic map operations (rendering, zooming, map rotation) but does them in a pretty robust way
• there seem to be support for styles
• haven't seen any more advanced functionality like POI, route display, overlay with tile data, etc.
• doesn't seem to be documented in any measurable way aside from basic build instructions
• and even the build instructions seem to be pretty ad-hoc, not to say fragile - they are Ubuntu-centric and expect to have one specific version (4.8) of gcc, otherwise you are out of luck (I have gcc 4.9 on Fedora 20 and haven't yet found a way how to force it to use it)
• the build system also looks pretty fragile - it is basically downloading & compiling some custom version of Mapnik and other libraries
• haven't seen anything resembling packaging anywhere so far
• so all in all while it is already remarkable what it can do quite a lot of work is needed to make it more robust and usable in real environment

The main question is - how do you actually use this to make a proper navigation app ? Currently it is basically just a demo that sets up a window and an OpenGL context that shows a map in it. It is open source so you could just take it and build your own application on top of it. But this would be rather tedious, as without using a proper GUI toolkit you would have to implement all the needed GUI primitives yourself, meaning that implementing any non trivial functionality would be quite a lot of work.

So basically what this needs to be actually useful is some sort of GUI toolkit integration. In this regard either Qt (as a QtQuick element or/and a QWidget) or SDL look like the best candidates. Once you have the integration, you can start building real apps with a really nice vector maps.

This is related to the question of how modRana can make use of the Mapbox map rendering widget.

ModRana currently has two main GUIs - the GTK2 GUI used mainly on the N900, the Qt 5 GUI used mainly on the Jolla + the semi inactive Qt 4 GUI used on Harmattan. If someone makes a QtQuick 2 element based on the Mapbox renderer (which I would say is quite likely to happen), modRana should be able to use it to render the map layer with relatively minor changes.

And if someone is crazy enough to both build it for Fremantle & to somehow integrate it with GTK2 (both are in my opinion unfortunately quite hard & unlikely to be done), it might even work with the GTK GUI with some modifications.