@fernandomaroto
Hi,
nice work! 
I have also done a simple user manager with yad. It seems to work, but is more limited than just using command line tools. And it does not have any bells and whistles, just a simple yad interface.
And naturally it needs much more testing to be reliable enough.
It can
- add a user
- delete a user
- modify user (in a very limited way): change user id, add to group, change primary group
- add a group
- delete a group
Does that sound anything useful for you?
EDIT: just noticed that it needs to inform user about errors more graphically… but no fatal errors so far 
System info to URL: (lspci; lsblk -fm; sudo blkid; sudo fdisk -l) | curl -F [email protected] https://ptpb.pw/?u=1
System journal to URL: journalctl -b -0 | curl -F [email protected] https://ptpb.pw/?u=1