Tile38 is an open source (MIT licensed), in-memory geolocation data store,
spatial index, and realtime geofence. It supports a variety of object types
including lat/lon points, bounding boxes, XYZ tiles, Geohashes, and GeoJSON.

Features:

    Spatial index with search methods such as NEARBY, WITHIN, and INTERSECTS.
    Realtime geofencing through persistent sockets or webhooks.
    Object types of lat/lon, bbox, Geohash, GeoJSON, QuadKey, and XYZ tile.
    Support for lots of Clients Libraries written in many different languages.
    Variety of client protocols, including http (curl), websockets, telnet,
        and the Redis RESP.
    Server responses are RESP or JSON.
    Full command line interface.
    Leader / follower replication.
    In-memory database that persists on disk.

WWW: https://tile38.com/