CPULoad offers a simple and light-weight possibility to have the state of your CPU readily available in your menu bar. If the load of your CPU looks suspiciously high, have a closer look at what is causing the load by launching Apple's Activity Monitor with a single mouse click. Activity Monitor lets you look at the process details and you may terminate the rogue process if required. More information about CPULoad can be found here.
Before there was Doom, Ultima, Rogue, or even Zork, there was... Adventure.
There were other text computer games before Adventure, such as STARTREK and WUMPUS, but this was the first of its kind; the first text "interactive fiction" game. It may seem outdated and quaint by today's standards, sort of like seeing the Wright brothers' original flyer parked next to a Boeing 747, but many of us remember it fondly. More information about Adventure can be found here.