One of the popular methods for creating websites, web applications and even web multiplayer games today are REST APIs. This technique allows for decoupling of a client application from the server.
Laravel is the most popular PHP framework for building web applications. It provides simple solutions for common problems, like secure database querying, routing, console commands, ORM or input validation. It is a very solid choice if you wish to follow test-driven development process.
Test-driven development is a concept of writing application code after writing tests. It requires from a developer to first define what is the expected outcome before starting the implementation.
Bitmasks are a very useful way to compress multiple boolean flags in a single variable. It can reduce memory usage and operations on bits are basically as fast as they can get. In practice, any time you want to have multiple flags describing something in your application, a bitmask could be the right tool for the job.
It can be quite hard to find inspiration to make an interesting small game, especially if you want to keep your scope small and finish it in a reasonable time frame. Here you can find some ideas to boost your creativity.