uMap
umap.openstreetmap.fr
OpenStreetMap-based map creator for building custom maps with markers, lines, polygons, layers, and embeddable interactive views.
Why it is useful
uMap is one of the simplest ways to publish a custom map without buying into a heavyweight GIS stack. It is ideal for event organizers, researchers, local guides, nonprofits, and anyone who wants shareable, editable maps with their own data layers. The ability to sketch something useful quickly and embed it anywhere gives it a sweet spot that many mapping tools miss.