These check tools are:
- online (so are always ready to run in seconds, and you don't need to install anything on your PC)
- free
DNS Health by Pingdom
A comprehensive test for global DNS configuration. Can be used for undelegated DNS servers
Zonemaster
Another comprehensive test, complete and fully configurable.
Dig Web Interface
Extensive web interface to dig for doing online dns / nameserver query.
What's my DNS
Global DNS propagation checker
