Open Historical Map (OHM) (http://www.openhistoricalmap.org) is an effort to use the OSM infrastructure as a foundation for creating the world's most universal, detailed, and out of date map. OHM will focus on the mapping elements where OSM excels - shores, political boundaries, buildings, and ways. Future and other efforts may engage in discussing actions, events, people, and movable items.

OpenHistoricalMap.org is currently under maintenance, we hope to get it up before the end of April 2014.
Please poke Tim at tim+ohm@geothings.net if it isn't!
In the meantime, feel free to sign up to the Mailing List: http://lists.openstreetmap.org/listinfo/historic

More info about the project
http://wiki.openstreetmap.org/wiki/Open_Historical_Map