There are no sensors, so this board is perfect for displaying information, patterns, animations, and status indicators. However, the LEDs are bigger and more spread out, so they fill the entire board. Like the Sense HAT, Pimoroni's Unicorn HAT packs an 8x8 LED matrix. It is not a full sized HAT as it is made for the Pi Zero, but it will fit on top of any modern Pi.
Similarly, a new board from Pimoroni, the Enviro pHAT, is handy for collecting environmental sensor data. See my articles on exploring the Raspberry Pi Sense HAT the Astro Pi competition and the Astro Pi flight case. The Sense HAT packs an 8x8 colour LED matrix and a set of environmental sensors. It was made for a specific event: it was sent to the International Space Station with European Space Agency (ESA) astronaut Tim Peake, and used in experiments coded by school children as part of the Astro Pi competition. The Sense HAT is another official product from Raspberry Pi.
See my recent article How to build projects using the Raspberry Pi camera. IR cameras are commonly used in wildlife and plant photography.
The IR version lets you see in the dark when you have an infra-red light source. There is a visible light version, and an infra-red (IR) version. The new V2 camera was released earlier this year: it is 8 megapixels and has a brilliant quality Sony sensor.
It uses the camera serial interface (CSI) port, which is present on almost every Pi model, to connect a small camera board to the Pi using a ribbon cable. The camera module is an official product of the Raspberry Pi Foundation. In no particular order, here are my favorites. Not all add-ons are HATs add-ons come in multiple shapes and sizes. The HAT specification gives specific dimensions to fit neatly on the Pi, aligning mounting holes, and holes for accessories suchs as cameras and display cables.