It's a new notification app for Nostr by nostr:nprofile1qqsxg45ph8gx0vdrvtzta6xal7v86frx6jvstsnvhrlvtehmwwh4epqpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhsz9mhwden5te0wfjkccte9ehx7um5wghxyctwvshsz9mhwden5te0wfjkccte9cc8scmgv96zucm0d5hspv33ka. It runs as a persistent service and attaches to your inbound relays. As soon as a qualifying event hits your relays, it triggers a notification that you can then click on and go straight to it in your client. It's still alpha software, but it's been really great so far.