What paid software have you replaced with something you built yourself?

So one of my collegemates, He mentioned that he had built an internal erp for a client that replaced a tool that the company was using that cost them around 5k a year and I was mindblown.

Have any of you made a tool that has replaced a software? I am not asking about the basic stuff like " I rebuilt Notion" , or the scheduling tool that someone had posted here recently. Something of real value that replaced something. What did it take y'all to build.

Author: LeadingJuggernaut892