ZeeMaps quickly maps point data on Google base maps in two ways:
1) The user uploads a .csv file of data points and their locations.
2) A group of users all add their own data location points to the map, on their own time from their own devices.
Each point can include text, video, image, or audio annotations.
Basic functionality is free; larger uploads and large numbers of maps require a paid subscription.

Ushahidi Platform

Ushahidi is an open source software for information collection, visualization and interactive mapping, to build tools for democratizing information, increasing transparency and lowering the barriers for individuals to share their stories. It has been used for election monitoring, crisis and emergency response, civil society, city/community building, arts and even where to find the best burger.

Specific tools:

Crowdmap: A simple map-making tool, built on an open API, that allows for collaborative mapping