diff --git a/doomsday/libdeng2/include/de/core/app.h b/doomsday/libdeng2/include/de/core/app.h
index 0cdfb94506..9ea3936bd6 100644
--- a/doomsday/libdeng2/include/de/core/app.h
+++ b/doomsday/libdeng2/include/de/core/app.h
@@ -25,6 +25,7 @@
 #include "../CommandLine"
 #include "../NativePath"
 #include "../LogBuffer"
+#include "../System"
 #include "../FS"
 #include "../Module"
 #include "../Config"
@@ -47,7 +48,7 @@ class Archive;
  *
  * @see GuiApp, TextApp
  */
-class DENG2_PUBLIC App
+class DENG2_PUBLIC App : DENG2_OBSERVES(Clock, TimeChange)
 {
 public:
     /// The object or resource that was being looked for was not found. @ingroup errors
@@ -88,6 +89,24 @@ class DENG2_PUBLIC App
      */
     void initSubsystems(SubsystemInitFlags flags = DefaultSubsystems);
 
+    /**
+     * Adds a system to the application. The order of systems is preserved; the
+     * system added last will be notified of time changes last and will receive
+     * input events last (if others don't eat them).
+     *
+     * @param system  System. Ownership kept by caller. The caller is
+     *                responsible for making sure the system has been
+     *                initialized properly.
+     */
+    void addSystem(System &system);
+
+    /**
+     * Removes a system from the application.
+     *
+     * @param system  System to remove.
+     */
+    void removeSystem(System &system);
+
     /**
      * Adds a native module to the set of modules that can be imported in
      * scripts.
@@ -225,6 +244,14 @@ class DENG2_PUBLIC App
      */
     void handleUncaughtException(String message);
 
+    /**
+     * Events received from the operating system should be passed here; the
+     * application will make sure all subsystems get a chance to process them.
+     */
+    virtual bool processEvent(Event const &);
+
+    void timeChanged(Clock const &);
+
 protected:
     /**
      * Returns the native path of the directory where the application can store
diff --git a/doomsday/libdeng2/src/core/app.cpp b/doomsday/libdeng2/src/core/app.cpp
index 53e5e5ed51..b4bdc96ca7 100644
--- a/doomsday/libdeng2/src/core/app.cpp
+++ b/doomsday/libdeng2/src/core/app.cpp
@@ -57,6 +57,9 @@ DENG2_PIMPL(App), DENG2_OBSERVES(Record, Deletion)
     /// Primary (wall) clock.
     Clock clock;
 
+    /// Subsystems (not owned).
+    QList<System *> systems;
+
     /// The file system.
     FS fs;
 
@@ -91,6 +94,8 @@ DENG2_PIMPL(App), DENG2_OBSERVES(Record, Deletion)
 
     ~Instance()
     {
+        clock.audienceForTimeChange -= &self;
+
         DENG2_FOR_EACH(NativeModules, i, nativeModules)
         {
             i.value()->audienceForDeletion -= this;
@@ -244,6 +249,30 @@ void App::handleUncaughtException(String message)
     if(d->terminateFunc) d->terminateFunc(message.toUtf8().constData());
 }
 
+bool App::processEvent(Event const &ev)
+{
+    foreach(System *sys, d->systems)
+    {
+        if(sys->behavior() & System::ReceivesInputEvents)
+        {
+            if(sys->processEvent(ev))
+                return true;
+        }
+    }
+    return false;
+}
+
+void App::timeChanged(Clock const &clock)
+{
+    foreach(System *sys, d->systems)
+    {
+        if(sys->behavior() & System::ObservesTime)
+        {
+            sys->timeChanged(clock);
+        }
+    }
+}
+
 NativePath App::nativePluginBinaryPath()
 {
     if(!d->cachedPluginBinaryPath.isEmpty()) return d->cachedPluginBinaryPath;
@@ -391,9 +420,23 @@ void App::initSubsystems(SubsystemInitFlags flags)
     // Update the wall clock time.
     d->clock.setTime(Time());
 
+    // Now we can start observing progress of time.
+    d->clock.audienceForTimeChange += this;
+
     LOG_VERBOSE("libdeng2::App %s subsystems initialized.") << Version().asText();
 }
 
+void App::addSystem(System &system)
+{
+    d->systems.removeAll(&system);
+    d->systems.append(&system);
+}
+
+void App::removeSystem(System &system)
+{
+    d->systems.removeAll(&system);
+}
+
 void App::addNativeModule(String const &name, Record &module)
 {
     d->nativeModules.insert(name, &module);
diff --git a/doomsday/libgui/include/de/gui/guiapp.h b/doomsday/libgui/include/de/gui/guiapp.h
index c62079c10c..1b5b84bb11 100644
--- a/doomsday/libgui/include/de/gui/guiapp.h
+++ b/doomsday/libgui/include/de/gui/guiapp.h
@@ -68,6 +68,9 @@ class LIBGUI_PUBLIC GuiApp : public QApplication, public App
     /// Emitted when the display mode has changed.
     void displayModeChanged();
 
+protected slots:
+    void refresh();
+
 private:
     struct Instance;
     Instance *d;
diff --git a/doomsday/libgui/src/guiapp.cpp b/doomsday/libgui/src/guiapp.cpp
index af81484a28..9c1cfd4f18 100644
--- a/doomsday/libgui/src/guiapp.cpp
+++ b/doomsday/libgui/src/guiapp.cpp
@@ -18,19 +18,28 @@
 
 #include "de/GuiApp"
 #include <de/Log>
+#include <de/math.h>
 
+#include <QTimer>
 #include <QDesktopServices>
 
 namespace de {
 
-struct GuiApp::Instance
+DENG2_PIMPL(GuiApp)
 {
+    TimeDelta refreshInterval;
+    bool loopRunning;
+
+    Instance(Public *i) : Base(*i),
+        refreshInterval(0),
+        loopRunning(false)
+    {}
 };
 
 GuiApp::GuiApp(int &argc, char **argv)
     : QApplication(argc, argv),
       App(applicationFilePath(), arguments()),
-      d(new Instance)
+      d(new Instance(this))
 {}
 
 GuiApp::~GuiApp()
@@ -62,14 +71,28 @@ void GuiApp::notifyDisplayModeChanged()
 
 int GuiApp::execLoop()
 {
+    d->loopRunning = true;
     return QApplication::exec();
 }
 
 void GuiApp::stopLoop(int code)
 {
+    d->loopRunning = false;
     return QApplication::exit(code);
 }
 
+void GuiApp::refresh()
+{
+    if(!d->loopRunning) return;
+
+    // Update the clock time. App listens to this clock and will inform
+    // subsystems in the order they've been added in.
+    Clock::appClock().setTime(Time());
+
+    // Schedule the next refresh.
+    QTimer::singleShot(de::max(duint64(1), d->refreshInterval.asMilliSeconds()), this, SLOT(refresh()));
+}
+
 NativePath GuiApp::appDataPath() const
 {
     return QDesktopServices::storageLocation(QDesktopServices::DataLocation);
diff --git a/doomsday/tools/shell/shell-gui/src/qtguiapp.cpp b/doomsday/tools/shell/shell-gui/src/qtguiapp.cpp
index 63a733ee45..5890ed2b22 100644
--- a/doomsday/tools/shell/shell-gui/src/qtguiapp.cpp
+++ b/doomsday/tools/shell/shell-gui/src/qtguiapp.cpp
@@ -65,4 +65,3 @@ bool QtGuiApp::notify(QObject *receiver, QEvent *event)
     }
     return false;
 }
-