How to connect a web app to a database to save and load data from that database

I am building an app that allows users to create a profile and start creating projects and adding data to these projects. I need the data that the users add and create in the app, to be saved in their account (on my database). Additionally, i want to offer collaboration on projects so that multiple users can view friend's projects and add and remove data, so the content is shared in real time.

I've already build the entire front end of this app (90% done), the design, functionalities.

Simply put, i am wondering what is the best tool i can use to accomplish this app. Wordpress? Codeigniter? Freestyle it?

(If this can be fully done in wordpress, that would be my preference, let me know if its even possible.)