How do you follow-up/track your leads?

I'm working on an MVP, mostly for a friend's company need of a software where you can track/follow-up leads and create different tracking flows depending on the campaign you're working on.

I'm working on a Zapier like tool but focusing into the lead/marketing space. We're going to support different channels for communication and different entry point (apps) for leads.

I did some research before starting building this but I want to hear some opinions on this project.