Both map renderers Tangram-ES and Maplibre-GL - https://github.com/tangrams/tangram-es and - https://github.com/maplibre/maplibre-gl-native are also written in C/C++.
Finally, most routing software, such as OSRM or Valhalla are written in C/C++.
If you notice something not covered by existing https://github.com/streetcomplete/StreetComplete/issues - feel free to report it.
Some glitches in map rendering are https://github.com/tangrams/tangram-es/ bugs, but in the worst case issue will be transferred/closed.
Web Renderer: https://github.com/tangrams/tangram Native/Mobile Renderer: https://github.com/tangrams/tangram-es
Native renderer can be accessed for android through gradle, ios through cocoapods and even available on raspberry pi.
Scene file documentation: https://github.com/tangrams/tangram-docs https://mapzen.com/documentation/tangram/ (still seems to work :D)
Scene file authoring tool: https://github.com/tangrams/tangram-play Which continues to live at http://tangram.city/play/
One of the great features of tangram is to embed any glsl shader in the scene file, which gets injected during rendering and "transforms" the map rendering and the map experience to a all new level, giving the some great flexibility cartographer/designer/developer will like.
As an example check this demo "tron" scene: https://tangrams.github.io/tron-style/#15/37.7926/-122.4003 (source: https://github.com/tangrams/tron-style)
Tangram had some great consumer base including this amazing project called StreetComplete (https://github.com/westnordost/StreetComplete/). Check it out and use it to improve osm street data.
Also mapzen's geocode engine Pelias, continues to live as geocode.earch, which it out at https://geocode.earth/.
Disclamer, I used to work for mapzen on the tangram-es (native rendering) project and still supporting the project in the open source world (along with other tangram-es developers).
If anyone interested has any questions, you can contact me @tallytalwar on twitter.