The UK Ordnance Survey’s “open data’ free product, free for all uses:
Code-Point Open is FREE to view, download and use for commercial, educational and personal purposes.(via Antoin)
Interestingly, they claim that IPv6 tends to be more reliable and has lower latency now:
Based on our testing, this makes our Happy Eyeballs implementation go from roughly 50/50 IPv4/IPv6 in iOS 8 and Yosemite to ~99% IPv6 in iOS 9 and El Capitan betas. While our previous implementation from four years ago was designed to select the connection with lowest latency no matter what, we agree that the Internet has changed since then and reports indicate that biasing towards IPv6 is now beneficial for our customers: IPv6 is now mainstream instead of being an exception, there are less broken IPv6 tunnels, IPv4 carrier-grade NATs are increasing in numbers, and throughput may even be better on average over IPv6.
lest we forget — this is a 2014-era writeup of OpenPostcode (open), Loc8 and GoCode (proprietary) as alternative options to the Eircode system
handy step-by-step clickthrough guide
Excellent HN thread re automated anomaly detection in production, Q&A with the dev team