There are a number of different legal stimulants which could be taken either for the improvements in cognitive function and focus, or perceived energy (as well as the performance benefits associated with that) and for these purposes there are no legal products which can match up to caffeine.
Ginseng is one commonly recommended alternative but no good evidence exists for it improving energy (certainly in the same way as caffeine does) and guarana is simply a source of caffeine much like chocolate or coffee beans.