dns.toys exposes small utilities through crafted DNS names, including currency conversion, world time, IP echo, number-to-words, and a usable slider range.
Drink is Stéphane Bortzmeyer’s experimental authoritative DNS server: query different names and record types for dynamic answers such as greetings, client addresses, and diagnostics.
DNS tunnelling encodes data in query names and answers to create a constrained communications channel, a pattern with both legitimate and harmful uses.
dnscat2 carries a full TCP/IP session through DNS and supports interactive traffic such as files and messages; its DNS-like appearance makes monitoring important.
A browser tunnel encodes arbitrary request strings in DNS subdomain labels and reconstructs them at the far end, showing the overhead of HTTP over DNS.
DNSKV is a generic public key-value service: names identify keys and DNS answers return values, backed by caches distributed across recursive resolvers.
DNSFS layers filesystem operations over DNS and resolver caches; its author demonstrated the design by streaming an MP3 through the DNS-backed filesystem.
NUM built a DNS data protocol with an SDK and npm modules; its Yellow Pages example retrieves structured company contacts through public resolver infrastructure.