Pretty much any image editor - especially powerful photo editing software such as
Photoshop or
GIMP - can be used for creating your own pixel art and textures.
However, there are others (but I can't remember any specific ones at this point in time) that are more specifically tailored to Pixel Art or animation, if that's what you're looking for. They are similar but have more focussed workflow for pixel art and the like.
For creating level maps (using the textures you created using the software mentioned above), you could use tilemap editing software such as
Tiled or
Mappy.