I LOVE Aseprite, I've been doing some artwork for games using it and it's been a great experience.
Whilst it's open source and you can build it for yourself, you can pay $10 for it and get a built version. The lead dev, David Capello, has been working on this project full time since March 2015 so if you enjoy it, I'd encourage you to pay for it.
And people actually pay rather than download a compiled binary? I've sometimes advocated that this could be a viable business model for an open-source project, maybe even have the license forbid redistribution of binaries, but each person I've proposed it to basically said the expected outcome is for people to just download the (illegal) binaries and give you no money.
Humans instinctively like things that are clever or well-made, and tend to want to reward that; it's just a matter of where that bumps into the desire to get more for less.
A quick glance at the source reveals a thing of beauty. Definitely a good reference for anyone looking for inspiration from a well-managed C++ project.
For those wondering how it's possible for it to look consistent across platforms and maintain that crisp, retro look, its' running Allegro 4 [1].
Libraries like SDL, Allegro, SFML, etc. are normally associated with games, but there are cases where it can used for creative tools as well.
Schism Tracker [2], an open source recreation of Impulse Tracker [3] uses SDL to deliver a cross-platform app. Like Aseprite, it also can be part of one's tool belt for making an awesome retro game, since tools like that are great for chiptune/8 bit/16 bit beats [4].
On a related note, the creator of Impulse Tracker, Jeffrey Lim also released the full source code 2 years ago [5].
Not that I've used Asesprite, and since its completely possible to avoid this I might be just spreading FUD or something, but one reason to avoid using something like SDL, Allegro, SFML, GLFW, etc, for a desktop application is that the style you typically use to write those (update at 30 or 60fps always) has very poor power consumption.
When you don't care about this, it opens up a lot of possibilities for making your life easier though. Immediate mode UIs are an easy way of getting what is basically a poor man's reactive data binding, and while they don't necessitate this style, they work best with it (and avoiding it with them can be a little tricky).
But again, never used Aesprite so I can't say if it does this. My suspicion would be that it doesn't! It's worth keeping in mind as a tool though.
Actually neither OpenGL nor DirectX force you to do this - it's just what game loops set out to do. There isn't anything stopping you from calling Present as infrequently as you want (i.e. when something changes).
What you are saying might hold truth because most people don't think about power consumption and could thus end up using a normal game loop for their UI app.
http://imgur.com/VIKM2Wj - I have Asepite open with two huge Vladstudio wallpapers and Photoshop and Blender just idling (nothing open). Photoshop CC and Blender register a higher energy impact in OS X.
New features get added all the time. If you do try Aseprite and find any problem with it, definitely file an issue. I haven't seen any feedback on power consumption, I imagine due to it being relatively smaller in footprint to other apps graphic artists use. There's probably a lot potential to make it better.
I acknowledge your point regarding using those libraries also. In the context of Aseprite and Schism Tracker, the aesthetic plays an important role. Aseprite is for pixel art and its' interface is deliberately done so, Schism Tracker wants to recreate the old DOS app Impulse Tracker. Customizing that to work cross-platform with a widget toolkit probably wouldn't pan out or be nearly as flexible.
And it's free if you compile it yourself from source; Linux binaries are also provided for free [1]. But I love it so much I was happy to chip in a bit toward development.
[1] Don't use version in the Debian repos - resizing the window doesn't work.
It's good stuff, I've used this quite a bit, although I still prefer macpaint for 1bit graphics (this is more geared for slightly higher palettes). Love the pixel perfect line tool.
My main gripe is the non-native UI. It makes it clunky to use imo. Pyxel edit also has that faked UI made in flash but it's not clunky, anyway. My favorite editor is Tile Studio but unfortunately it doesn't really support alpha transparency properly at all and animation is annoying at best.
I think they drunk too much of their own Kool-ade. Pixel sprites can make for a great, retro aesthetic, but using them for a full UI (including fonts) is too much, IMO. Watching the video, looking at the pictures; it's a lot of strain on the eyes due to the poor anti-aliasing and having to parse out a font I haven't used in decades.
Whilst it's open source and you can build it for yourself, you can pay $10 for it and get a built version. The lead dev, David Capello, has been working on this project full time since March 2015 so if you enjoy it, I'd encourage you to pay for it.