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GIT is one of a group of publicly accessible repositiories for software, firmware, and documentation which implement 'versioning'. Versioning keeps track of changes to files and let's one follow those changes, revert to previous versions, and create branches so that varieties of the code can be made, and also merge branches back into the main branch.
Wiki entry: https://en.wikipedia.org/wiki/Git_%28software%29
Comparison between sourceforge vs github: http://recomparison.com/comparisons/101554/sourceforge-vs-github/
This is a company that has written a Microsoft Basic program to control a model railway from a computer.
Is a common point in circuits normally 0 volts, but can be higher than 0 volt.