While GeoServer is one of the most popular options, there are other great alternatives for publishing spatial data and interactive mapping applications, such as MapServer. You can find more information about MapServer at the official website at http://mapserver.org.
GeoServer is an open source server for serving geospatial data. WMS is georeferenced images used to display data that can't be easily represented using markers. An example is meteorological data such as clouds, winds, or surface heat maps.