favorite network troubleshooting tools (online)

hey there, I recently have come across this http://ping.pe/ website, I have no association with this but it's pretty awesome. This made me wonder what other tools out there which I do not know about it. what are your favorite network troubleshooting tools? In addition to ping.pe, I like https://bgp.he.net but would love to hear your thought about other tool recommendations as especially the ones that are distributed. Mehmet