A cheap and small 360 degree camera capable of 5 mpixel still images and full HD video. Prices vary greatly but you can get it for as low as 75€ Amazon.de (August 2018).
This is truly just a camera module with lenses and sensors and nothing else. It has a USB C plug in the bottom and you plug it into your phone to use. It makes use of an OTG USB connection and at least in OnePlus 6 you allways have to go to settings to enable OTG because it will be disabled automatically after 10 minutes for security reasons. This makes using the camera a bit of a hassle but even worse is the fact that since the camera plugs into the USB connection at the bottom, you have to keep the phone up-side-down when using.
The software is not great but it gets the job done. The image quality is decent although not great. The two images created by the camera are stitched together well but the resolution just isn't quite enough.
The camera comes with a small soft pouch and I wish it would have come with a custom hard plastic case just the size of the camera. I could very well carry this camera around in my jeans pocket all the time since it's smaller than my Google Pixel Buds case that I also carry.
The camera itself is not only small but also slippery. Very, very slippery. Handeling it is like handeling a bar of soap - while holding your phone. Although I tend to be extremely carefull with my gear I ended up dropping this camera on the second day, scratching one lens.