Wikipedia believes Tormenta (Portugese for 'Storm') is a campaign setting usable with either Wizard's d20 system or 3D&T. The publisher, however, seems to indicate the Tormenta core book presents a complete RPG system. What's going on with that?
Tormenta is both an RPG system and a campaign setting
The Tormenta article isn't about a specific book or book line, it's about the setting that is found within the books. Notably it's not an article titled “Tormenta RPG”, the article is just titled “Tormenta” (no italics), and the article confines itself to information regarding the setting's existence.
What's unusual here (speaking as a semi-retired Wikipedia administrator) is that it's very uncommon for a Wikipedia article about a setting to exist unless the setting is very noteworthy all on its own, separate from the RPG it serves. Even the setting for Rifts has no independent article despite being subject of two RPG systems (Rifts and Savage Worlds), and just exists as a subsection of the article “Rifts (role-playing game)”.
But though that's unusual, it may just be due to the casual pace of Wikipedia's editorial process. It may be destined to be merged with the 3D&T article, or transformed into a Tormenta RPG article with the setting being only a subsection, or simply removed as insufficiently documented by secondary sources to satisfy Wikipedia's (a tertiary source) governing policy on what subjects may be included in the encyclopedia. Of note, the Tormenta article has a pair of notices indicating that it has citation problems, which means the latter might be the case, and it might be destined for removal as “not notable”.
So to sum, what's going on is:
There is a product page for a book called Tormenta RPG (English translation by Google). It appears to contain both RPG rules, and material about Tormenta-the-setting. There appear to be various supplements. So ‘Tormenta’ is the name of an RPG, as well as the name of a setting.
The Wikipedia article only concerns itself with documenting Tormenta-the-setting's existence. It doesn't take any position regarding whether “Tormenta” is also an RPG or just a setting, concerning itself only with the setting.
Tormenta is primarily a D&D 3.5 adaptation with a deep lore, but...
...you don't have to go deep on it in your campaign, a lot of stories have vague statements like "the location of this legendary weapon is curently unkwown" to be used as cliffhangers on adventures, but the universe can work very well without using characters, items and events from the book.
The ruleset is a great improvement on D&D 3.5 in my opinion, being less "magic item dependant" and more "player choice dependant".
PS.:There's tormenta systems based on other classics, like Pathfinder, but the D&D 3.5 based is the main one.