The ruling party does not have to have only 33 % or so to rule. In fact, there's no need for ONE party to rule. Switzerland is a good example. Government and opposition practically don't exist (there is one party, who partly tries to create such an environment, but the population is against this). Instead we have all big 4 parties involved in government all the time (we have 7 Bundesräte (=Presidents), that makes 2-2-2-1 per party, which is called the 'Zauberformel' (or was, cause in last election, two parties switched sides (the CVP got one bundesrat instead of two and the SVP vice versa)). And this system works since 1848.
Besides these four parties, there are many more.
mfG mitsho