Is there a Software (Windows or Linux) to monitor the Wifi of every computer of the home network.
Sometimes my connection is slow, I would like to know which computer make it slow.
I think my o2 Box can t do it...
A quick check showed at least half a dozen apps in the Ubuntu repository that will allow you to monitor per-node and per-user bandwidth use. Some of them will allow you to regulate users' bandwidth -- this is called "Traffic Shaping". Check your router, too, because some of them also allow traffic shaping.
I'm sorry I'm not being more precise about it -- much depends on your network setup. Your next step will probably be to read up on which apps you can use, and use the one that best fits your situation.
tbbMeter from Think Broadband will do what you want for Windows:
[Not a real answer but too large for a comment, but I hope some folks will find this information useful and consider upvoting it anyway.]
Any time this kind of question comes up, I feel someone needs to point out that most tools that report bandwidth are stuck in the 1990's, where most networks had a single signaling rate, so the machine that sent the most bytes used the most bandwidth.
That is not true of Wi-Fi. On Wi-Fi, one device might be farther away where it only gets the slowest data rates, or it might be an older 802.11b device even up close, and it can take as much as 450 times the airtime of a modern 3-stream 802.11n client to send the same number of bytes in optimal conditions.
So unless your bandwidth-measuring tool is Wi-Fi-aware and tells you want percentage of the airtime is being used by each device, you'll probably need to take its output with a grain of salt.