Is it possible to add custom actions to files and folders within our organization?

So looking to add either to the actions menu for files / folders.. or maybe create a custom app that we can use to accomplish the same things.. Just need to know which route to head down and start looking into.. 

If adding to the action menu is possible, what is a good source to get started?

If that is not possible, what is a good source to review on creating an app that simply allows you to bookmark key items within the org. 

We have found a app within the appstore in teams called TagMyFav.. but requires creating accounts for everyone and a little over kill for what we want/need.

We want the basics, like in your browser, where if I want to bookmark this site, i simply add to bookmarks and can place it in a folder structure to manage it. Even though this app would be available to everyone in the company, it would be local to their own teams application, just like every browser.