Guarana soda pop is ubiquitous in Brazil and often available at tropical groceries here. It's really tasty and packs a wallop. Guarana wakes you up like crazy, but it doesn't cause coffee jitters. It is possible that in addition to caffeine, there is some other substance in guarana that also produces an effect, since it 'feels' different than coffee. Same goes for mate.
Caffeine is an alkaloid.
These compounds have different biochemical effects, and are present in different ratios in the different plant sources. These compounds are very similar and differ only by the presence of methyl groups in two positions of the chemical structure. They are easily oxidized to uric acid and other methyluric acids which are also similar in chemical structure. Diuretic, smooth muscle relaxant, cardiac stimulant, vasodilator. The presence of the other alkaloids in colas and tea may explain why these sometimes have a stronger kick than coffee.