Spark: Puzzles for the Curious is a free iPhone app designed to stimulate curiosity through daily puzzles. The app offers a variety of themes that cover topics such as history, pop culture, science, geography, and sports. Users can enjoy fresh puzzles every day without the pressure of timers, focusing instead on the joy of discovery. Spark encourages a fun habit of learning something new each day, making it a unique addition to the educational app category.

One of the standout features of Spark is its human-crafted puzzles, which are designed to evoke 'aha' moments rather than being generated by algorithms. The app includes tools to help users track their progress, reinforcing the habit of curiosity. As part of a suite of mental fitness applications, Spark aims to strengthen cognitive abilities while providing an enjoyable experience.