Guayusa (ilex guayusa) is a plant native to the rainforest in Ecuador, traditionally cultivated and harvested by the Kichwa and Jivaro tribes, who dry the leaves and brew them into an energy drink.
Guayusa is now becoming popular world wide as a caffeinated herbal tea with a reputation for inducing lucid dreams.
Theobromine (found in chocolate) is a heart stimulant, and lowers blood pressure by dilating your blood vessels.
L-Theanine (found in green tea) moderates the effects of caffeine, letting you have the energy and focus but without the spikes and jitters.
(One important ingredient of tea and yerba mate that is not found in guayusa is theophylline, a stimulant that raises your blood pressure, the opposite effect of theobromine.)
Here is a summary of products and ingredients:
Calm Energy (and Lucid Dreams)
It's the combination of caffeine and L-theanine that lets guayusa give you alertness without the shakes - relaxed focus, calm energy.
Guayusa is available at some retailers; see this locator for Runa in particular.
Guayusa is also available online:
This National Geographic article gives the basics of guayusa, and shows the link between guayusa and dreaming in Kichwa mythology.
This Daily Beast article describes the traditional cultivation and use of guayusa by the Kichwa.
Some tea experts review Guayusa at Teaviews.
For the effects of L-theanine combined with caffeine, see this study on focus, a Beginner's Guide to Nootropics, and an article from Tea With Gary. (There is also a supplement with L-theanine and caffeine.)