NuGet is an open source initiative that 'Makes it easy to install and update open source libraries in Visual Studio' or so it says on the website. Basically its a Visual Studio plugin that allows you to add packages to individual projects. These packages can contain different things such as assemblies, commonly source files etc. With support for both an online public repository as well as the ability to use local repositories it makes it a good way to save your libraries, even if it is only for your self or your team.