How to create Web Applications using WordPress! Part 2

Before we left off, in the first article of the series about creating web applications using WordPress, I recommended to search and install some plugins. The plugins are to save us a lot of time of coding. Those plugins are Advanced Custom Fields and Custom Post Type UI, both free but with premium features to pay for if needed.
However is our class, we will not need any premium feature. It’s our zeal to develop something that will allow us the opportunity.
Looking at the web application we shall build.
It’s always good to plugin before developing anything that will used by people. Because what we are building must be a solution to a problem.
For this tutorial we shall develop a web application where we can store and retrieve book keeping records easily, without using a pen and book. So the basic features of our application will to record our budget, Cash out and Cash In. Since other people like friends and family could also be suffering with book keeping, we shall also allow anyone to register for an account on our system, allow them to login and able to record and retrieve their records.
Which means we need a user management system but WordPress has one already. All we need is to show a registration and login forms to the user.
For that case we need a plugin. But which is that among the many that exist! Before I mention and recommend I would like to hear your opinion.
Thanks for reading and contributing!