I think this is what you are talking about:
https://togs.com (support the original makers not random knockoffs)

I haven't used them but they seem like a cool idea. Most of my flat bars these days are Koga Denham or Velo Orange Crazy Bars so the need is maybe lessened.

SQ Labs makes a different version more akin to actual bar ends:
https://www.sq-lab.com/en/products/innerbarends/