vtm VS eraser-map

You are correct, Valhalla is used for routing. Maps are rendered on the ELEMNT, BOLT and ROAM with mapsforge, BOLT2 with vtm. To look at map files there is cruiser cruiser (mapsforge) and cruiser-gl (vtm). Create updated maps with wahooMapsCreator. There is also some documentation how to add POI's or make a custom theme.

for an example. It's perfectly smooth. The application is closed source but the underlying renderer (VTM) is LGPL3. The renderer, https://github.com/mapsforge/vtm, is basically an OpenGL alternative for the mapsforge offline maps format and maintained by the same guy (the original mapsforge renderer is arguably a bit slow, struggling to hide its slowness behind cached tile bitmaps).

(Former Mapzen employee here).

I _think_ you're talking about Eraser Map(https://github.com/mapzen/eraser-map) right?

It was awesome! It's the closest I know of to "Google Maps, but open source and based on open data". It was an app built for _end users_, not OSM editors. And it worked pretty darn well. When it didn't, any problems could (at least theoretically) be addressed with improvements to OSM data or the Mapzen open-source projects.

There was a team of at least two people working on it full time, plus lots of work on the design, product, and integration with geocoding, routing, transit etc. The multi-modal (switching from walking to transit to car, etc) transit directions were particularly awesome.

I used it as my daily driver for much of my navigation around NYC, and as time went on only had to fall back to Google Maps maybe 25% of the time, usually for missing POI data.

Unfortunately I think it's one of the few Mapzen projects that hasn't seen new life after the company shut down, and like you said it would take quite a bit of work (read: money) to keep it going. It might be possible with some work to find grant money through a couple organizations. The OSMF has done some awesome work lately with the micro-grants, but this would definitely be a level we haven't seen (yet).