I hacked a simple service for gathering HN replies and organizing them by the parent's username.
The main idea is to be able to efficiently get the latest replies to an HN user. For example, you can use this service to send yourself notifications when some replies to you on HN.
The service queries the official HN API and can be self-hosted. It is basically ~30 lines of Bash script. I made this mostly for educational purposes -- thought you might find it useful for something.
Cheers!
Edit: for example, here are the latest replies to me [0]. It includes only recent replies, since I started the service just yesterday and it hasn't observed older replies.