Esri has actually shared open source projects before, but they’ve been strewn across many different services. It seems the GeoIQ for ArcGIS (is that a thing yet?) guys are getting this all organized.
We’ve got the ball rolling already with several repositories up and running on Github. Esri’s presence in Github centers around two separate accounts: http://github.com/esri and http://github.com/arcgis. The “esri” account will house (host?) code that is meant to be more freestanding and generic. Code that a has broad reach to very more non-GIS community like visualization examples, solutions and various other scripts will all live there. The “arcgis” account will house open source code related directly to the “ArcGIS Platform” and have repositories for things like ArcGIS Online templates and ArcGIS Desktop extensions. The structure of all the code and repos will grow and evolve as Esri places more code on Github
I’m not sure I totally get why there needs to be two (why not just use the Esri one?), but it sounds like this is a work in progress. I’d just assume follow the Esri one and wait for ArcGIS projects to filter in.
I’ll just hit F5 until the projects are all in one repository.