Love it, sends me an e-mail for keywords on Reddit.
I've been using F5Bot to track the mentions of both SaaSHub and LibHunt for quite some time now. It is super simple to set it up and remarkably fast. What is more, it's free and you don't have restrictions on the number of terms to monitor.
The only drawback is that it monitors only Hacker News and Reddit. Yet that's big enough in most cases.
Do you know an article comparing F5Bot to other products?
You can submit it here