Opta - Opta is a new kind of Infrastructure-As-Code framework designed for fast moving startups.
Ethereum Name Service - Like DNS, but for Ethereum wallet addresses
Chain - The Block Chain API for Developers
How DNS Works - Super cute web comics about 'How DNS Works' for beginners!
DNSPerf - Free DNS performance analytics
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.