What technical inventions and scientific discoveries appeared in Europe as a result of the Crusades?

The Europeans adopted from the Saracens a saber made of flexible steel (before they knew how to forge only heavy swords – it was hard to fence with them), a crossbow, powder mines (there were no guns until the XIV century), skills of chemistry (alchemy), Arabic numerals.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.