diff --git a/platform/viewer/src/appInit.js b/platform/viewer/src/appInit.js
new file mode 100644
index 000000000..a50d13782
--- /dev/null
+++ b/platform/viewer/src/appInit.js
@@ -0,0 +1,83 @@
+import {
+  CommandsManager,
+  ExtensionManager,
+  ServicesManager,
+  // HotkeysManager,
+  UINotificationService,
+  UIModalService,
+  UIDialogService,
+  // MeasurementService,
+  // utils,
+  // redux as reduxOHIF,
+} from '@ohif/core';
+
+import buildModeRoutes from './routes/buildModeRoutes';
+
+/**
+ * @param {object|func} appConfigOrFunc - application configuration, or a function that returns application configuration
+ * @param {object[]} defaultExtensions - array of extension objects
+ */
+function appInit(appConfigOrFunc, defaultExtensions) {
+  const appConfig = {
+    ...(typeof appConfigOrFunc === 'function'
+      ? config({ servicesManager })
+      : appConfigOrFunc),
+  };
+
+  const commandsManagerConfig = {
+    /** Used by commands to inject `viewports` from "redux" */
+    getAppState: () => store.getState(),
+    /** Used by commands to determine active context */
+    getActiveContexts: () => getActiveContexts(store.getState()),
+  };
+  const commandsManager = new CommandsManager(commandsManagerConfig);
+  const servicesManager = new ServicesManager();
+  // const hotkeysManager = new HotkeysManager(commandsManager, servicesManager);
+  const extensionManager = new ExtensionManager({
+    commandsManager,
+    servicesManager,
+    appConfig,
+    api: {
+      contexts: CONTEXTS,
+      hooks: {
+        useAppContext,
+      },
+    },
+  });
+
+  servicesManager.registerServices([
+    UINotificationService,
+    UIModalService,
+    UIDialogService,
+  ]);
+
+  /**
+   * Example: [ext1, ext2, ext3]
+   * Example2: [[ext1, config], ext2, [ext3, config]]
+   */
+  extensionManager.registerExtensions([
+    ...defaultExtensions,
+    ...appConfig.extensions,
+  ]);
+
+  // TODO: Init global hotkeys, or the hotkeys manager?
+  // TODO: We no longer use `utils.addServer`
+  // TODO: We no longer init webWorkers at app level
+  // TODO: We no longer init the user Manager
+
+  // TODO: After extensions are registered, add modes and datasources to buildModeRoutes.js
+
+  const { modes } = appConfig;
+
+  const routes = buildModeRoutes(modes, extensionManager);
+
+  return {
+    appConfig,
+    commandsManager,
+    extensionManager,
+    servicesManager,
+    routes,
+  };
+}
+
+export default appInit;