Big O is an Android application that provides users with a comprehensive reference of run-time complexity for common data structures and sort algorithms. With this app, users can easily access information about the efficiency of different algorithms and make informed decisions when designing or optimizing their own code.

In addition to the reference material, Big O also offers a speed testing feature. Users can run tests to compare the run-time performance of various data structures and sort algorithms. This allows developers to experiment and find the most efficient solution for their specific needs.

Overall, Big O is a valuable tool for developers and computer science enthusiasts who want to understand and optimize the performance of their code. With its user-friendly interface and extensive information, it is a must-have app for anyone working with algorithms and data structures.