Historypin

Historypin is a digital, user-generated archive of historical photos, videos, audio recordings and personal recollections. Users are able to use the location and date of their content to "pin" it to Google Maps. Where Google Street View is available, users can overlay historical photographs and compare it with the contemporary location.
This content can be added and explored online.
There were formerly a series of smartphone applications, but these were discontinued as of 2015 latest.
The project was created by the non-profit company Shift (formerly We Are What We Do), as part of their inter-generational work, with funding and support from Google as part of a series of commitments to digital inclusion. The website has over 200,000 assets and recollections "pinned" to the Historypin map around the world, with higher contributions in the UK, USA and Australia. The beta version of the website was launched in June 2010 at the Royal Institute in London by Nick Stanhope, CEO of Shift and the full project was launched at the Museum of the City of New York in July 2011.
Collections.
The website features a range of themed collections, some of which commemorate historical events. Previous collections include:
Contributors.
As well as user-generated content, material has been added to the site from museums, local history societies, historical photo archives, newspaper archives and businesses. Contributors include Biggleswade History Society, Bishopsgate Institute, The John Lewis Partnership, Mirrorpix, The New York Transit Museum, PhillyHistory.org, The Ritz Hotel, Baltimore Museum of Industry and the Science and Society Picture Library and the Albright-Knox Art Gallery.