Yes, with Trackingplan you can monitor both your websites and apps. However, keep in mind that, if this is your business case, installations for both web and app will be required.
For websites, you can install Trackingplan using Google Tag Manager or by adding the snippet at the top of the <head> section of your website.
For apps, you’ll just need to install Trackingplan’s iOS and/or Android’s SDKs directly.