Pixel Art

Resources

Pixelorama | Orama Interactive
Tilemancer by Led (retired)
Tilesetter - Tileset generator & map editor tool - $13 Bring in a few tile sprites and generate a complete tileset automatically. Seems a bit fiddly to get set up, but perhaps it has templates.
Tiled Map Editor | A flexible level editor - Popular. Well-documented.
Online-Tile-Map-Editor - Very basic editor for map based tiles. Can load multiple tilesets, and place tiles in layers. No transformations, so no flip/rotate for e.g.
tIDE: Tilemap Integrated Development Environment - Windows only.
Ogmo Editor 3 - Scans everything in the project folder, so creating a project in an existing folder with existing files can completely choke it up. Poorly implemented UI (for e.g, no copy/paste in text fields, no undo). Layers, entities, decorations. No tile transformations, so no flip/rotate.
Atlas Tile Editor (ATE) on Steam - Early access. Not very polished for a $5 app.
Pixel Studio - $12.99, Mac App Store.
Pixel Studio for pixel art on Steam - $8 on iPad, or $12 on iPad for cross-platform license. Doesn't look like they have a website. Powerful and feature complete. Painful to look at. Good selection of palettes, pixel perfect pencil, layers, animation, etc. Pro version includes a tile mode but not sure how useful it is.
PixaTool by Kronbits - $15 (on sale). Generates pixel art from any image. Examples are impressive, but was not able to reproduce in a few minutes of playing with the demo app. Worth another look.um

Tileset automation:

Tileset Gen by Eduardo
Autotiler - TileSet Autotile Generator by route1rodent - 3€
ASCII Mapper by No Time To Play - Draw maps with ASCII characters
Random Tileset Generator by supernapie - Generate tilesets based on randomizing assets and colors
Tilekit by rxi - $20 "Tilekit is a tilemap editor centered around pattern-based auto tiling."

Generation:

Sprite by tversteeg - Looks like a basic free version of CryPixels CryPixels by CrySoftware

Dithering:

PicoPalette by RhythmLynx creates dither patterns for all combinations of PICO-8 colors.
Dither Machine by Lunar Labs - Dither Machine is a tool to help you generate dithering automatically, instead of doing it by hand, which can be a tedious task.

Pixelation:

RetroEditor by zxretrosoft - Windows only. Comes with a ton of presets for different conversion targets (color palettes) including obvious things like different consoles and games and more obscure references like film and tv, art history, design, etc. Pretty awkward UI.
Pixelizer by Digisims Windows only. The examples on the Itch page look pretty bad.
Pixel Fluffer by Mathbear - "Pixel Fluffer is a useful tool to enhance your basic pixel sprites".

Animation:

Paint of Persia by dunin - A very clever app that can overlay a pixel art canvas on top of any video or image, using it as a reference for rotoscoping.

Color:

Misc:

Mappy Tile Map Editor - A utility for creating flexible 'maps' for 2D and 3D tile based games - Windows only. Very little detail.
Pickle - Adobe Air app. Paid. Had tools for creating tilesets and animations.
Tile Studio - Windows only. Some pretty cool tools for drawing with gradients, creating color conversion scripts. Auto tiling feels a bit clunky.
FontSprite by AdamStrange and FontMap by AdamStrange - what's the distinction between fonts and tilesets?
Playscii - an open source ASCII art and game creation program - ASCII art