Both Pixelmator and Acorn are now 16-bit.
Neither have adjustment layers per se - yet. The developers of Acorn, though, have told me that adjustment layers are coming- just a question of when.
Today, both apps give you a very useful 'layers-for-lightroom' alternative.
Additionally, they both support the BC_imageunit plugin which give you more refined image control than standard. And in the case of Acorn, it's a non-destructive workflow, allied with a price drop from 49.99 to 29.99