An open source application by definition is software that you can freely access and modify the source code for. Open source projects typically are worked on by a community of volunteer programmers.
A historical GIS is a geographic information system that may display, store and analyze data of past geographies and track changes in time. It can be regarded as a subfield of historical geography and geographic information science.
Terra is a multi-national NASA scientific research satellite in a Sun-synchronous orbit around the Earth. It is the flagship of the Earth Observing System (EOS). The name “Terra” derives from the Latin word – Earth.