I made an online tone generator based on the Firefox Audio API. It’s basically a large logarithmic slider that allows real-time, smooth frequency changes. You can also fine-tune the frequency in 1 Hz increments, if necessary.
There are other tone generators on the Web, but they are not as cool (if I do say so myself) and/or they require Java or Flash.
Warning: my generator only works on Firefox. Due to a bug in the Linux version of Firefox, it doesn’t work on Linux.
What can you use a tone generator for? You can do a science experiment with resonance, tune a musical instrument, test the limits of your hearing (I can hear nothing above 19,000 Hz, even at maximum volume), or figure out your tinnitus frequency to better target therapy.

That’s why I love this blog: Tom always posts something cool. Thanks Tom!
It’s bad luck for me. I use linux. :D grrr But it’s good toy. Nice one.
So I try it in Ubuntu 12.04 with firefox 15.0 and it works propably bad. I listen good 20hz to 20173hz. Is it this bug? Does it give bad sound?
Are you saying you tried it in Firefox 15 on Ubuntu and it works? It doesn’t work on Firefox 14.
It’s not working for me in Firefox 18 under Windows 7. The controls are there (minus the frequency number), but I can’t interact with them.
Thanks, fixed. There was a syntax error in the JS — I don’t know how I managed to upload a non-functional file — I always test my sites after I upload them to the server.
Physics will never explain things like this.
Have you thought of giving users the option to change the phase of the signal so that they could possibly reduce or cancel the sound from another device. I have tinnitus and would like to see if it is possible to use this method to reduce the level of the sound in my head.