[browningstreet]

On mobile but the first thing I did was search page for “marble”. Not found. These seem like digital marbles.

[dannyking]

This guy beat me to that! https://www.youtube.com/watch?v=8uHtffYrXww

[MildlySerious]

The website linked in the description is down, and digging up the Twitter account, the last tweet is from Feb 7 saying the marbles are "nearly ready".

Looks to me like that niche is not filled yet after all!