I personally am using geekpay right now. They dont service the note for you, its just a platform for managing them. I have mine linked to stripe for downpayments and atcum for ach deposits.
The platform offers a way for customers to login and see their amortization tables etc. It also automates emails about payments/past due etc. Very easy to use.
I have heard of others using cozy as a free option, although it technically is set up for rental property.
A fellow investor in a master mind group i am in sends all his to Madison note servicing for 20 bucks a not per month and its hands off for him.