Based on what you've laid out this app would need to:

1.) Allow a user to create an account
2.) Allow a user to log in and out of that account
3.) Allow a user to change/reset their password
4.) Allow a user to create a "sheet"
5.) Allow a user to edit their own "sheets"
6.) Possibly allow a user to view other users' "sheets"

I do not know of anything that does all of this (and only this) though WordPress could likely be forced into the role via plugins/etc. I would not recommend that course.

It sounds like most of the work here if you were to build something from scratch would be the user management and permissions. Something like userfrosting (if you use PHP) might help you get a head start on the process since it takes care of those parts. Then you would just need to add on the CRUD (create, read, update, delete) for your sheets. If your programming language of choice is something different let me know, there are projects similar to this one for most languages and they can save you a ton of time.

This is great. Thank you so much. Also what i am looking for is bit similar to Job seeker's role, job seeker log in, create resume/form, then submit, but they can also edit and view their submitted resumes whenever they want. Do you know any open source project like that? I love this community here, so helpful everyone is!!!

Hey, I explore the UserFrosting a little bit, it might just be able to take care of the user interface part. However, I will still need "Form" part that can handle complicated calculation for user to fill out online.
Do you know if there is any open source program that can act like a Form and be able to be connected well with UserFrosting? Thank you very much for your help.