Network Topology Mapper

Network Topology Mapper is a free open-source browser-based network diagram editor. You place device types on a snap-to-grid canvas, draw the connections, and import or export the map as JSON. Cloud sync is optional, so the editor still works if you never sign in.

David Kiener made this project. The credit for it stays with him. The live app and the project page are on VWS Digital, and the same tool is listed from the open-source page.