as mentioned above "Wireless Tether for Root Users", is the best I have found. I have also heard barnicale(sp?) is pretty good too. you might have to find a specific wpa_supplicant file for your device that you want to tether to, if you want to connect to say a tablet.
I don't know why but for some reason Google Android after it reached a certain OS they didn't want us to tether from our phone to our tablets. I was not able to until I got the modded wpa_ file and dropped it in the correct folder with root explorer, I'm just speaking on the tablets I have tried and that at least 10 of them I don't know if it will work with other tablets because it is a Honeycomb and ICS issue, that's got the file that needs replaced, so I would think all newer tablets need this modded wpa file, Probably because they are trying to sell 3 and 4G tablets so they don't want us to connect with our phone you can find more info if you Google WPA_SUPPLICANT but it can be done just find the modded wpa file for your device, you will need root access to drop the modded wpa file into the device your trying to tether to.
Now as far as for computers it will pick up right away you wont need the modded wpa_supplicant file. If you have a wireless connection on your PC you will see a new connection called something similar to AndriodTether.