Sitecore Package Installer through code. You store packages under /Packages folder. Call the controller through /utility/installpackage.

Global.asax.cs

using System.Web;
using System.Web.Mvc;
using System.Web.Routing;

namespace Site.Web
{
    public class MvcApplication : HttpApplication
    {
        protected void Application_Start()
        {
            RegisterRoutes(RouteTable.Routes);
        }

        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.MapRoute("InstallPack","utility/installpackage", new {controller = "Utility", action = "InstallPackage"});
        }
    }
}

PackageInstallController.cs

using System;
using System.IO;
using System.Linq;
using System.Web.Mvc;
using Sitecore.Data.Engines;
using Sitecore.Data.Proxies;
using Sitecore.Exceptions;
using Sitecore.Install.Files;
using Sitecore.Install.Framework;
using Sitecore.Install.Items;
using Sitecore.Install.Utils;
using Sitecore.Publishing;
using Sitecore.SecurityModel;

namespace Site.Web.Controllers.Shared
{
    public class UtilityController: Controller
    {
        public JsonResult InstallPackage()
        {
            var installer = new PackageInstaller();
            var hasChanges = false;
            var logFile = Sitecore.MainUtil.MapPath("/Packages/PackageInstallLog.txt");
            var status = string.Empty;
            if (!System.IO.File.Exists(logFile))
            {
                try
                {
                    System.IO.File.Create(logFile).Close();

                }
                catch (Exception ex)
                {
                    status = "Installation failed. " + ex;
                }
            }

            //Get Files
            var fileEntries = Directory.GetFiles(Sitecore.MainUtil.MapPath("/Packages"));
            var logEntries = System.IO.File.ReadAllLines(logFile);

            
            //Install Plugins
            foreach (var fileName in fileEntries)
            {
                if (fileName == logFile)
                    continue;
                var isInstalled = false;
                foreach (var installedPackage in logEntries)
                {
                    if (fileName.Equals(installedPackage))
                        isInstalled = true;
                }
                if (!isInstalled)
                {
                    try
                    {
                        installer.InstallPackage("/Packages/" + fileName.Split('\\').Last());
                        System.IO.File.AppendAllLines(logFile, new[] { fileName });

                        status += "Installed: " + fileName + "<br/>";
                        hasChanges = true;
                    }
                    catch (Exception ex)
                    {
                        status = "Installation failed" + ex;
                    }
                }
            }

            status += "<br/>Installation succeeded";
            if (!hasChanges)
                status = "You are up-to-date!";

            return new JsonResult
            {
                Data = status,
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
        }
    }

    class PackageInstaller
    {
        public void InstallPackage(string path)
        {

            Sitecore.Context.SetActiveSite("shell");
            using (new SecurityDisabler())
            {
                using (new ProxyDisabler())
                {
                    using (new SyncOperationContext())
                    {
                        IProcessingContext context = new SimpleProcessingContext();
                        IItemInstallerEvents events = new DefaultItemInstallerEvents(new BehaviourOptions(InstallMode.Overwrite, MergeMode.Undefined));
                        context.AddAspect(events);
                        IFileInstallerEvents events1 = new DefaultFileInstallerEvents(true);
                        context.AddAspect(events1);
                        var inst = new Sitecore.Install.Installer();
                        var filePath = Sitecore.MainUtil.MapPath(path);
                        var pkgFile = new FileInfo(filePath);

                        if (!pkgFile.Exists)
                            throw new ClientAlertException(string.Format("Cannot access path '{0}'. Please check path setting.", path));
                        inst.InstallPackage(filePath, context);
                    }
                }
            }
        } 

    }
}