In Wikirunner there are two players: a chaser and a runner. The chaser has to reach the same page the runner is on using the internal links of every Wikipedia article. The runner has to escape the chaser by using the internal links as well.
Seems simple, right? In practice, it's not easy at all. Aside from the difficulty of finding the right link in every moment, you also have to take into account the time. If you take too long to find a link that can lead you to the runner, the other player could click on a link that's completely different from the ones you're following, making you start over from scratch.
It should be noted that Wikirunner uses only the English version of Wikipedia. So if English isn't your first language, you might find the game a bit too difficult.