Currently you can load up to 4 of your favorite Android applications with the official ARC runtime.
By default the chromeos-apk tool replaces the Vine application and everytime you load a different app it replaces it. However you can load 3 more apps by replacing Evernote and other apps. For each extra app adjust the "key" value in the manifest.json file of that app, then use "Load unpacked extension...".
Chrome OS: With Chrome 38+ you can now side load as many applications as you want. If you have older apps that
were created using chromeos-apk tool then re-convert them or remove the "key" option from manifest.json.
Windows, Linux and OS X: To load unlimited number of apps on you need a custom runtime, see the ARChon runtime guide for details.