Math, medicine, astronomy, physics.
While the Catholic church was banning original thought these folks were inventing the modern world. Unfortunately Catholicism evolved, Islam has not :/
I do think the meme that Islam contributed a bunch of scientific achievements is a bit not based in reality. Its like one of those commonly assumed and repeated little fabrications with enough truth in it to really stick around. The fact is that the vast majority of what Islam is credited with contributing in terms of scientific achievements to the West was actually just captured from the Byzantines and other Greek controlled territories and then preserved, or relayed through Arabic societies as a go between, such as the concept of zero, which was actually developed by the Hindi first, and paper, which was developed in China originally, both then propagated down the Silk Road to the West through Arabic cultures and Islamic societies. The Islamists get credit for preserving what Europeans would have otherwise squandered, however. For instance, the only remaining copies of writings by people like Aristotle were held and cared for by Islamic and Arabic rulers for an extended period, and the only reason we have those manuscripts today is directly because of Islamic care for them.
Further, the idea that only Catholics were condemning and silencing scientists is also incorrect. Al Raza was persecuted and condemned as a blasphemer for not worshiping the Islamic traditions exactly. The Taqi al-Din was built not long after the Muslim conquest of Constantinople and was torn down by the Caliph not too awfully long after that due to pressure from Islamic clerics in Istanbul and the failure of his chief astrologer to properly interpret the appearance of a major comet in the sky that was followed by a plague. That's not to say that Islam is devoid of scientific contributions, but rather, that their contributions are overly exaggerated to some extent. Coffee (not really science but there's a lot of science that wouldn't get done without it!), as well, was popular among Africans, Arabs then adopted it from their African slaves, but get credit for "discovering it" for some reason.
Even most major Islamic monuments outside of the Ka'ba were built with Byzantine knowledge, training, laborers, and craftsmen, etc.
I really think the BBC is the reason so many people today think the West just would not be where it is scientifically without Islamic contributions, because of this show, which, while technically accurate, gives a sort of one sided view of exactly how much Islamic scholars contributed to modern scientific knowledge.
Islam really is an insular thing, and the vast majority of its scholars throughout history, and today, are/were educated in and graduated with doctorates in areas like religious theory, not scientific backgrounds.
They (Islamic scholars) did, however, contribute much of the core mathematical theories which Copernicus and later Galileo used to fuel their discovery, so they certainly deserve credit for that.