Pixelmator - Layer groups are visualized as a stack of the grouped layers so they are easy to identify.
This is just one reason I love Pixelmator. Compared to Photoshop, it’s an absolute breath of fresh air. So much thoughtfulness, innovative thinking, and attention to detail. It also totally lacks the bloat and sluggishness that Photoshop is famous for. I can’t possibly recommend it enough, and it’s only $30 in the Mac App store.