You can definitely create you own apps! Once you have them created you can add them to you Subscription Level App Catalog. Once they are added your users will be able to add them to their dashboards and custom pages by selecting them from the app catalog like they would for one of our Core apps.
You can find information about how to use the Subscription level App Catalog and how to add apps to it here Subscription Level App Catalog | CA Agile Central Help. Take a look when you have a chance and let us know if you have any questions.
Thank you very much for your help, blawe01!