I use Paint Tool SAI and since I bought the original version, I am able to use 2.0, which has very similar tools that Photoshop has, which includes all the different layer modes and text. But I've heard it is hard to work on Macs (its originally for Windows) so I would recommend FireAlpaca, which is basically the same as SAI, but has all the photoshop stuff BUT is 100% free, unlike SAI 2.0 is (unless you get a pirated copy) I, personally, am not a fan of GIMP bc I feel its too mediocre and doesn't work so well like Photoshop and such does, but I've heard from many people that once you get used to the program, they can do pretty good things with it. It half has to do with the program mechanics itself and half is yourself being an artist that makes the programs work well for you
So yeah, those are my recommendations
Hope they help!