Koop
Transform, query, and download geospatial data on the web
... including vector-tile, WMS, and plain old GeoJSON. Koop's plugin-architecture facilitates custom deployments specific to your needs. "Provider" plugins to connect to novel data formats and translate to a common format (GeoJSON), while "output" plugins then transform that GeoJSON to other specifications. See a list of plugins already authored and maintained here. If you have a novel data source or require an as-yet unsupported output format, new plugins can be easily developed and integrated.