CommaFeed

 CommaFeed  is an open source feed file reader that may request feeds as often as every 5 seconds, and has a js;dr homepage (commafeed.com).

Open source: https://github.com/Athou/commafeed

Every 5 seconds feed requests from: 148.251.41.232 (hosted by Hetzner) as of 2017-03-17 as observed in web server logs.