What tools do you use to drive customer success in your startup?

I am using usermaven.com to help increase adoption and reduce churn in my other products https://contentstudio.io and https://replug.io.

Disclaimer: Usermaven is my 3rd SaaS product.

I just use email, but I try my best to reply to emails as quickly as possible. Users seem to appreciate prompt responses and I have a feeling 70% of the users that email me eventually buy a subscription