Teenage Engineering OP-1, a music synthesizer. Really well built, buttons and knobs feel fantastic, and the display is super fun. The OP-1 in action: https://www.youtube.com/watch?v=umatbZ0n4mE
I wanted to suggest another option that is much less expensive and worth checking out if you are interested in this type of music is Teenage Engineering Pocket Operators [1]. These are just a fun instrument/toy to play around with and they only cost $50! From the same company too...I wouldn't say the Pockets are a "best-design thing" but I do think they are an easy and inexpensive way to start messing around creating your own music on a hardware instrument before deciding on a bigger purchase like a $1000k synthesizer. The website is great and has sample sounds of each model:
FWIW it works quite well if you connect it to a MIDI host and use another controller to play or sequence the synths on it.
...just don't connect your 12v AC adapter to the OP-1's USB hub that wants 5v, or you'll lose all data connectivity (USB disk mode and MIDI) to the unit. :(