There are a few different things that come to mind when thinking about what would be considered "cool as fuck" when it comes to technology.
One option could be the Philips Hue lights - these are smart lights that can be controlled via an app and can change to any color imaginable. They can also be set to certain 'scenes' or ambiances, such as a 'relaxing' scene which would dim the lights and change the color to a calming blue. They are a really fun way to add a pop of color or change the mood of a room, and can be found for under $100.
Another option could be a wireless charging pad. These are becoming increasingly popular as they add an extra level of convenience - no more fumbling around with cords! They work with Qi-compatible devices and can charge them just by being placed on top of the pad. They come in a variety of styles and colors, so you can find one that fits your aesthetic.
A final option could be a smartwatch. These are watches that pair with your smartphone and can perform a variety of tasks, such as displaying notifications, tracking fitness activity, and controlling music playback. They come in a range of styles and prices, so you can find one that meets your needs.
So, those are a few different options for tech that is "cool as fuck" and under $100. What would you consider to be cool and under $100?