Top 4 map-viewer open source projects

Create your own 2D Maps with layer-by-layer system using Noise-Sample and BufferedImage pattern

Android App to view Locations in a map with support for gpx, kml and kmz data

WebHL is a fork of hlviewer.js that uses the File System Access API to load game assets direct from your computer rather than from a server.

An openlayers-based modern map viewer for MapGuide