Saw this Camera from Sony the RX0 II, released in March of this year. It has the insides of a Sony RX100 V inside and is smaller than a GoPro. 1 inch sensor shoots 4k at 30fps. Looks pretty interesting in what it can do. The biggest downside is no continuous AF but for a matchbox sized camera this looks pretty cool.
Not really an action camera per se but more like a small powerful camera. I have to say that the tiniest aspect peaks my interest.
Sidd