Chrome: If you're in a library or cafe with spotty Wi-Fi, the Chrome Connectivity Diagnostics app can tell you if the problem is your PC, the local network or the internet beyond. It's fast, surprisingly flexible and free.
As its name implies, the Chrome Connectivity Diagnostics add-on is available in the Chrome Web Store. It runs a battery of tests from your browser to see if it can connect to the internet. It checks for an active connection, tries to reach your DNS server, checks for any firewalls or portals that may be blocking traffic (such as hotel login portals that require you to accept terms of service before you can connect), tests for DNS resolution delays, and finally tries to reach Google to test for network delays. You can run the tests automatically, and whether they pass or fail you can always click on one to see exactly what the test did and more detail about the results.
The Chrome app isn't as powerful or flexible as other network diagnostics tools designed for administrators or more tech savvy users, but it is fast, it's free, it runs from Chrome's App Launcher (meaning you don't have to install any additional software beyond Chrome), and it's incredibly simple to use, which makes it perfect for troubleshooting other people's PCs or giving to someone who may look to you for tech support. Hit the link below to download it.