This project is part of ASP.NET Core. You can find samples, documentation and getting started instructions for ASP.NET Core at https://docs.asp.net.
The repository is used to create multiple ASP.NET Core Docker images. Follow the links below for more details on each image.
microsoft/aspnetcore-buildmicrosoft/aspnetcoremicrosoft/aspnetcore-build-nightlymicrosoft/aspnetcore-nightly
FYI: the microsoft/aspnet image has moved to https://github.com/Microsoft/aspnet-docker.