Quite frequently I've wanted to show people various fractals I've made and discovered. This usually translates into showing them some pictures on my phone that I made 3 years ago, showing them google results, or building and running a preview app with different equations and iteration methods.
Exposition is a showcase of fractals. Some are interactive, which allows you to see how the fractal changes over fields of complex numbers. There is a cursor which shows where in the complex plain the parameters is, click or drag to adjust it's location.
The app is written in Swift, and a bit of C++ for the shader code. The fractals are computed on the GPU using Metal 2. You can use guestures to scroll and zoom, and when you get lost click on View -> Reset. Finally, there's also Touch Bar support 😉.
Exposition runs on macOS High Sierra 10.13 (released in late 2017). It might work on previous versions but I haven't tested it.
The latest version can be downloaded from here.