checkwho.im
I've often found myself wanting to look at the information about my current connection and browser, such as my IP address, its reverse DNS info, and what headers my browser is sending. So I made a single-page site that does that.
Current stuff
These are my more recent creations:Older stuff
These are my older creations that might be unavailable or unmaintained:
Genmaicha
ARKcert
ArkSwitch
HashProp
Simple TLS
Xmlodic
Network Suite
Sonicasting