Are you sure it has to be online? I’ll say the BEST thing that has worked for me personally is a PC game called Mavis Beacon. You can find it anywhere. It’s a GREAT typing program that tracks your progress. You only have to do a little each day/every other day and you’ll start seeing results fast, within a week even. I know it’s not really “online” and I’m sorry, but this has worked for me and others and I just thought I would throw it out there. I recommend it to anyone wanting to improve their typing speed/accuracy.