A search engine for numerical data. The site offers access to several million financial, economic and social datasets (read: time-series). Quandl indexes data from multiple sources allowing users to find and download in various formats. All Quandl's data are accessible via an API. API access is possible through packages for multiple programming languages including R, Python, Matlab and Stata. An Excel add-in allows access to data, including stock price information.Quandl's sources include major IGOs, such as the UN, Worldbank, Eurostat etc, central banks, US bureaus and agencies, non-US statistical agencies, financial agencies and stock markets, think tanks and academia, and private sector sources..Source: Wikipedia, accessed 2016-02-03
Varies by time-series.
Selected list of data sources: https://www.quandl.com/blog/free-data-on-quandl
Online, interactive data resource.
Exports to Python, R, Excel.