One Word Domains - Database of all available one-word domains
intoDNS - IntoDNS checks the health and configuration and provides DNS report and mail servers report.
Tool.Domains - Search free to register expired domains
Dnsstuff - DNSstuff offers DNS tools, Network tools, Email tools, DNS reporting and IP information gathering.
Handshake.org - Decentralized certificate authority and naming
MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.