Check out also Kosmtik, https://github.com/kosmtik/kosmtik, which is a similar alternative and which many in the OpenStreetMap community have shifted to using.
We use maputnik now because we want the style to be MapBox GL and not CartoCSS: https://github.com/maputnik/editor. We use the MapBox client libs, but host the vector tiles and styles ourselves. Raster tiles seem so 2010 :)
MapBox hired the maintainer of maputnik though, so the future is unclear.
MapBox hired the maintainer of maputnik though, so the future is unclear.