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wellcome to OSM Terrarius 
Well the visualisation is quite ‘easy’ by using an POI overlay or an own rendered full map overlay
http://wiki.openstreetmap.org/wiki/OpenLayers_Marker_Example
http://wiki.openstreetmap.org/wiki/Rendering
But well the user contribution is quite difficult. OSM actually is unable express the time in our modell
http://wiki.openstreetmap.org/wiki/Comparison_of_life_cycle_concepts
You might use other technologies like a Mediawiki based approach or a own OSM DB server to which the users contribute.
Someone else did something similar by inventing own technologie: http://www.kleks-online.de