map tiles

OpenLayers

OpenLayers is a Javascript library that can display map tiles and markers loaded from any source in web browser. It provides an API for building rich web-based geographic applications.

Modest Maps

Modest Maps is a small Javascript library for interactive tile-based maps that can display maps from external sources (e.g. OpenStreetMap, but not commercial layers like Google Maps), enable panning and zooming, and track the position of points based on XML data. It is designed to be lightweight and offer a minimal set of features, and therefore has less functionality than Leaflet, a similar tool.

TileMill

Open source map design studio for creating and styling web tile maps, based on either provided free MapBox Geodata, or data imported as a variety of file formats. It uses the CartoCSS styling language to customize interactive visualizations, with powerful control of symbols, zoom levels, labels, and other cartographic details. The finished maps can be exported either as images or tiled web maps. Though the TileMill software is free, there may be a fee to host the created tiles on MapBox or elsewhere.

Mapstraction

Mapstraction is a Javascript library. It provides developers with a single interface for a wide variety of Javascript map APIs including Leaflet, Google, Bing, OpenLayers and ESRI's ArcGIS.
A key benefit is that once a developer has loaded Mapstraction, s/he can to switch from one map API to another quickly and easily - often only needing to change a few lines of code.
Mapstraction displays points, lines, polygons and markers on the maps, and also allows developers to add base maps and overlays.