Aseprite is an animated sprite editor and a pixel-art tool.
Pro Good selection of tools for animation
You can change the playback speed of the loop and the speed of each individual frame. There are three playback modes: forward, reverse, and ping-pong. Onion Skin mode is included to speed up the animation process and to allow for tagging the timeline to help keep animations organized. There is also a live preview so you can always see the end result.
Onion Skin mode will overlay previous and next frames over the canvas so you can use them as references when drawing. For Onion Skin mode, you can adjust items like range, opacity, and tint, whether the onion frames are in front of or behind the canvas, etc.
You can tag different parts of the timeline when, for example, you need different animations for the same character. You can then loop those tagged sections individually.
Pro Easy to use
Getting started with the program is straightforward. It's laid out intuitively: the main workspace in the middle, color selection on the left, tool section on the right, and animation timeline at the bottom.
All tools and the vast majority of functions have keyboard shortcuts, allowing for results to be obtained quickly.
Aseprite is a very focused program: it's not filled with icons, there's no excess functionality, and dialog boxes generally only have a couple of options so you're never overwhelmed and it's easier to learn.
Pro Very intuitive thus easy for complete beginners
The interface invites you to be creative, and since it's pixel art you are creating, this adds to the feeling of being in the right environment. Everything seems to have its natural place and thereby could make beginners feel right at home.