Gudgeon is a caching/blocking DNS proxy server. What sets Gudgeon apart is the ability to segregate machines, subnets, and IP ranges into different groups that all receive different blocking rules. The motivation for Gudgeon comes from the proliferation of devices on my home network that belong either to outside entities (Google, AT&T, Amazon), kids, or unwise adults. Different groups, classes of user, and devices need different blocking rules.
Take, for example, a user who has shown persistent inability to avoid internet scams. You can assign that user's machine(s) to group(s) that block more suspicious DNS requests. On the other hand you might want to allow a device like a Google Home or Alexa unit to have full access to the internet except for tracking/advert websites. You might want to create extensive blocklists to protect kids who use the internet from their devices.
For all of these reasons Gudgeon has been created to allow more flexibility in host-based DNS blocking.