Windows: Whether you're troubleshooting poor performance on your own wireless network or trying to figure out how overloaded the hotel Wi-Fi is where you're staying, Who Is On My Wi-Fi is a free Windows utility that can show you who else is using that precious bandwidth.
Once installed, Who Is On MY Wi-Fi lets you scan everyone on a given network (or set an IP range to scan). It tells you IP addresses, MAC addresses, computer names (if they're broadcasting) and connection status for each user. Usefully, the app doesn't require you to have administrative rights or access to the network to run.
If you're using your own home network and want to find out if someone's freeloading or has cracked your Wi-Fi password, you can just log in to your router and check. However, if you're using someone else's Wi-Fi, this app can come in handy. Before you fire it up and check your company's office Wi-F, keep in mind that it's essentially port scanning, which may or may not set off a few alarms with your IT department. You don't want to have to explain to your normally-friendly network security engineer why you've been mapping the company Wi-Fi with an unauthorised tool.
Who's On My Wi-Fi is free, and the video above shows you how it works. It requires Microsoft. NET framework to run, and you can grab it at the link below.