Guaraná (gwah-rah-NAH) is derived from a berry (Paullinia cupana) found growing throughout a swath of Brazil ranging from the Amazon to Bahia. The seeds are ground and used widely in products as diverse as a popular Brazilian soft drink (called “Guaraná” of course), to the capetas (little devils) served at drink stands, to “energizing” açai, to ampules of liquid (Arrebite is a popular one) which can be purchased in farmácias for an energy kick. The ground powder itself can be purchased in farmácias for use as one sees fit (added to homemade vitaminas or simply stirred into water or a soft drink).
The “thing” about guaraná is its energizing property, and there is some polemic about this in that the boost from guaraná is somehow often perceived to be different from that derived from coffee. This has led a lot of people to believe that the energizing substance in guaraná is chemically different from caffeine.
What is different is that guaraná seeds have a high fat content, even after having been reduced to a powder. This fat slows down the rate of caffeine release, so that rather than the fast up (and down) provided by coffee, guaraná provides a much smoother and long-lasting ride. The flavor of the powder is pretty atrocious, but sweetened and in small amounts (per the soft drinks) it’s very pleasant.