TL;DR version: These are 29 military-style kinds of sprite and 6 kinds of building, with 8 palettes, 8 directions of facing, including isometric, an explosion animation for each of those, attack animations, and some bonus sprites for explosions and basic terrain. There's a total of 77,872 images. CC0-licensed. Preview here. Video of current sprites here.

EDIT October 2015: New versions available with smoother lines, more units, and generally a cleaner look. The new versions are split into an isometric version and an ortho version, and they are sized differently from each other (unlike these). If you want 8-way facing, you may still want to use these sprites, otherwise I recommend you check out the revised versions.

You might want to read the rest of this post if you want to understand how to use the animations a little better.

These sprites are part of my PixVoxel assets collection that I'm steadily building up. This set is meant for a less-serious wargame, with a visual style inspired by the Advance Wars franchise.  It includes 28 types of moving unit (plus a Civilian meant for story purposes or less-violent uses of these sprites), 6 types of building, firing animations for all of the units with weapons, and fiery death explosions for all of the units and buildings.  All graphics come in 8 palettes, have 8 facing directions, and are intended to be viewed on a normal isometric grid. They can also work without a grid for an RTS-type game, or can use only some of the directions to have it work on a hex grid. A preview of the isometric version, with enough animations to sometimes cause Firefox to crash, is available here.  A video of an open source game (code here) that I made with a partial set of these graphics (no boats or civilians) is available here.  My game isn't especially playable yet, so you should make your own with these!

The sprites are generated from voxel models (that I made over the course of about a month and a half) using an open source program I wrote, that is available here on Github. The firing animations and explosions are procedurally generated, using code to modify the voxel models' data without requiring changes to the model for each frame. The Github project also includes the voxel models in MagicaVoxel's .vox format, but the palettes in the model files are placeholders meant to be replaced by my program, so using the .vox files directly may not be as easy as using these sprites.

The directory structure is split into isometric (diagonally facing) and orthogonal (up/down/left/right facing), and inside each of those, into palettes named like color0 for standing animations, and a merged folder called animation_frames for other animations. Colors 0-7 refer to the palettes 0: Dark, 1: White (with alien-like soldiers and green fire), 2: Red, 3: Orange, 4: Yellow, 5: Green, 6: Blue, 7: Purple.  The naming convention for the mobile units (not buildings) is based around a concept of a base unit with three types of upgrades: Power, Speed, and Technique.  For example, there is a set of graphics for the Tank (with no upgrade), another for Tank_P (Power upgrade), another for Tank_S (Speed upgrade), and another for Tank_T (Technique upgrade). Non-attack, non-explosion sprites, including buildings that aren't exploding, are named like Tank_P_Large_face3_2.png , where Tank_P is the name of the unit, Large is a stand-in in case larger or smaller units are introduced, face3 refers to the facing direction (both isometric and orthogonal views use the numbers 0-3, but they refer to different rotations, both advancing clockwise as the number goes up), and the last number is the animation frame.  Attack sprites are named like color2_Artillery_S_Large_face2_attack_1_1.png , where color2 is the palette (as before), Artillery_S is the name of the unit, Large is a stand-in (as before), face2 is the facing direction (as before), attack_1 is which weapon is being used in the animation (see the file UNIT_INFO.txt for more info, but some units have an attack_0, some have only an attack_1, some have both, and some have none), and the last number is the animation frame.  Explosions are named like color7_City_Large_face3_fiery_explode_2.png , where color7 is the palette (as before), City is the name of the unit, Large is a stand-in (again), face3 is the facing direction (again), fiery_explode is always used for all explosions (it's intended to allow other kinds of death animations), and the last number is the animation frame.  There are also "receive animations" to be shown when a unit is attacked by a certain kind of weapon.  There are 8 kinds of weapon here: 0: Handgun, 1: Machine Gun, 2: Torpedo, 3: Cannon, 4: Long Cannon (for the Artillery), 5: Rocket, 6: Arc Missile (traveling down from the sky, and meant to be delayed from the firing animation), and 7: Bomb (a huge wave of fire extending from the bombs dropped by the Plane_P). Some kinds of weapons don't have different receive animations for all palettes; if a palette for an animation isn't present, it was identical to the color0 version and so it was removed. The receive animations are named like color3_Long_Cannon_face3_strength_1_10 , where color3 is the palette (of the attacker), Long_Cannon is the kind of weapon, face3 is the facing of the defender if he is looking at the attacker (meant to allow counterattacks to look smooth), strength_1 is a variant on the receive animation meant to be matched to an attacker (see UNIT_INFO.txt), and the last number is the animation frame. The file UNIT_INFO.txt has the information on what attack numbers, kinds, and reception strengths belong to which units.

To center a standing animation on one of the supplied isometric terrain, you need 20px x offset and 6px y offset, plus a varying amount, 3 times the depth of the terrain tile (see TERRAIN_INFO.txt).  I haven't used the ortho tiles yet in a game, so I can't be totally certain of the right offsets, but the (tripled) depths should be the same as iso.

This set is being released into the public domain under the CC0 license.  You can use it in commercial projects without any hassle, and can redistribute it without crediting me (though I, Tommy Ettinger, would appreciate being credited!).  It would be nice if you use these graphics to leave a comment here on OGA so I can see what people do with this art, but there's no requirement to do so.