Pngcrush

Pngcrush is a simple command-line utility that you can use to optimize image files with the PNG format. For example, you can change the resolution or compression. It packs advanced settings, so it primarily caters to users who have relevant experience with image editing tools.
While most applications come with a graphical interface that is clean and intuitive by popular demand, some users still prefer working with command-line programs, as they do not require installation, usually occupy a small size on disk, and typically let you perform a task in just a few lines, rapidly.
Once you launch this app in a Command Prompt dialog, there is no other way but to dive into its advanced settings, as listed when calling Pngcrush.
For example, you can modify the color type of the output file, establish the saving directory and new extension, alter the gamma, write the maximum IDAT size or a new MNG (without crushing embedded PNGs), as well as disable limits for the width, height, cache and malloc functions, among others.
As expected, the tool barely uses CPU and RAM, thus it doesn't affect the computer's overall performance. It has a good response time and carries out tasks rapidly. No error dialogs have been shown in our tests, and the app did not hang or crash. Thanks to the wide array of configurable settings, experienced users should make the most out of Pngcrush.