Pixel art is anything drawn in the medium of computer pixels, usually created one pixel at a time. Because of this, pixel drawings are usually done on a small scale to save time.
Isometric pixel art is the use of pixel art in an isometric viewpoint. Alternate or exaggerated perspective is rarely used in isometric pixel art, as it complicates the drawing process.
The are numerous computer graphic programs available today. Because of the relatively simple process of creating pixel art, one need not be picky about what they use to create it.
MS Paint will generally work well, though it lacks several features (translucency, layers) that more complex programs may provide
Photoshop or other programs of the sort (Paintshop Pro, GIMP, Krita) work well, though their line tools may use vectors or otherwise complicated methods of drawing. Many features (such as automatic anti-aliasing) must be turned off in order to pixel with these programs.
Programs designed specifically for creating pixel art are also available, such as mtPaint, GrafX2, and ASEPRITE. The latter is commercial, but open-source.
Pixen is a great free app for Mac users.
Pixelesque is a good pixel art editor for Android and Android-compatible systems(CyanogenMOD, Replicant). It is limited to art of 64x64 pixels or smaller.
