Aseprite

Aseprite is an open-source sprite animation program that allows users to create animated sprite and pixel-art. Aseprite is a sprite editor that affords users the ability to create 2D animations for videogames. It is used to create pixel-art, retro-style graphics, and/or any graphics desired by the user using the 8-bit (and 16-bit) generation of consoles. Aseprite is provided via Steam key for Windows and also provided as DRM-Free. For key redemption, a free Steam account is usually required. 

Features:

• It has an intuitive interface that allows affording any user its usage from beginners to professionals.
• It Composes sprites using layers & frames as separated concepts
• It Creates images in RGBA or Indexed color mode (256 colors), or Grayscale images
• It supports Windows XP, Vista, 7, 8, or 10 operating systems
• It opens and saves GIF animations, sequences of PNG files, ICO files etc.
• It has a timeline feature where users can copy and move layers, frames, or specific images
• It has animation tools for real-time animation preview, onion skinning, and tag frames
• It supports the Undo or Redo for every operation
• It has Pixel art tools for drawing patterns and textures, shading, for pixel-perfect traces or strokes, for RotSprite rotation, for tiled mode, and for filled contour or polygon
• It supports multiple editors and/or views for the same sprite.
• It has the capability of Exporting and importing sprite sheets
• It has a command line interface to automate conversion and for sprite sheets generation
• It supports updates for the whole v1.x series up to v1.9.
• It has a command line interface

Thus, Aseprite is a program that hobbyists, pixel artists or game designers can use because it is great for any level of work. Moreover, since it is designed for this set of people, it tends to be versatile while being stylish.   

Aseprite's intuitive interface makes it very easy for beginners to draw characters and layers.