GetInstalledPackages.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using NuGet.Frameworks;
using NuGet.Packaging.Core;
using NuGet.ProjectManagement;

namespace ConsoleApplication5
{
    class Program
    {
        static void Main(string[] args)
        {
            var projectDir = @"C:\Users\user\Documents\Visual Studio 2015\Projects\ConsoleApplication5\ConsoleApplication5";

            foreach (var package in GetInstalledPackages(projectDir).Result)
            {
                Console.WriteLine(package);
            }
        }

        public static async Task<List<PackageIdentity>> GetInstalledPackages(string projectFolder)
        {
            var project = new PackagesConfigNuGetProject(projectFolder, new Dictionary<string, object>()
            {
                { NuGetProjectMetadataKeys.TargetFramework, NuGetFramework.Parse("net46") },
                { NuGetProjectMetadataKeys.UniqueName, "test" },
                { NuGetProjectMetadataKeys.Name, "test" },
            });

            var installed = await project.GetInstalledPackagesAsync(CancellationToken.None);

            return installed.Select(e => e.PackageIdentity).ToList();
        }
    }
}