Solution level packages are deprecated in Visual Studio 2015. You can apply a package to a project and a simple way to achieve it is to create a project that will include what you used to apply to the solution level.

http://blog.nuget.org/20150729/Introducing-nuget-uwp.html

Too bad. Why removing a feature that is useful and doesn't harm? :-(

At my company we often create solutions with a predefined layer structure (interface, domain, infrastructure, tests) and we have a NuGet package that creates one project for each of these layers with the appropriate name and namespace depending on the solution name, plus adds a set of build scripts. With this change we will have to trash this, I can't see how we can use the "apply the same to a project" approach.

So we'll have to keep VS 2013 installed forever, just to apply this package to new solutions. That's crazy!

Nuget was never intended to be a visual studio scripter. What you could do instead is build a vsix.

Even applying package at project level not working -

PM> Install-Package xunit.runner.utility -Version 2.1.0
Install-Package : Project 'Default' is not found.
At line:1 char:1

Install-Package xunit.runner.utility -Version 2.1.0

CategoryInfo : ObjectNotFound: (Default:String) [Install-Package], ItemNotFoundException
FullyQualifiedErrorId : NuGetProjectNotFound,NuGet.PackageManagement.PowerShellCmdlets.InstallPackageCommand
PM>

That looks like an unrelated issue, please open a new bug and provide exact details on how to reproduce the issue. Please make sure you are using the latest nuget extension (3.4.4-rc at the moment)

I got it fixed now after following 'bitpen' 4 steps listed here - http://stackoverflow.com/questions/10130333/cant-install-packages-with-nuget-500-internal-server-error

Easiest way to fix this is to open a working vs2015 solution(create a new one if you don't have one) and try the Install-Package command again.