When you type 'test tools' in Google you can see a lot of links to Selenium, cURL, Cucumber or even Firefox. I agree they are useful, but we are testers, and we shouldn't test tools, but real systems. Below I give a lot of links to playgrounds, when you can train your skills. I hope this will help you to understand that you should always pair 'test tool' with system you test, not vice-versa. Also, in my opinion, by solving real problems you learn faster than by following tutorials.
