Balloons Tower of Defense 4, also known as Bloons Tower of Defense, is one of the few web games you can hack without actually having to know anything about hacking. No cheat engines or hacks you have to download - this game has a bucket full of glitches that frequently play to your advantage.
Take the BTD4 Expansion Version, for example. There exists a glitch that allows you to play one of the premium tracks (#6) without needing to pay for it using your coins. Have fun!