Gmaps4rails is developed to simply create a Google Map with overlays (markers, infowindows...). Yet it's backed on a very flexible codebase which could be prone to accept other map providers.

Use it with any Ruby app (I guess you could simply take the js anywhere if you like).

Basic map
One marker
Geolocation
Multiple Markers + auto-adjust + clustering
Multiple Overlays
Custom Style
Custom Builder
Kml
Directions