SpriteSheet from Layer Groups

1) To install, copy SpriteSheetGroups.scm to {GIMP-HOME}\share\gimp\2.0\scripts\SpriteSheetGroups.scm
2) Either close Gimp and re-open, or simply select menu: Filters > Script-Fu > Refresh Scripts
3) Load your images via File > Open as layers (select all the images you want to in the spritesheet)
4) Run menu option Filters > Sprite-Sheet > Create From Layer Groups...

Each group should have layers for that particular animation. The plugin will output each animation on a row from left to right.

Example Of a layer tree

 Run
   | - Frame 3
   | - Frame 2
   -- Frame 1
 Jump
   | - Frame 3
   | - Frame 2
   -- Frame 1

output will look like:

Run Frame 1     Run Frame 2      Run Frame 3
Jump Frame 1   Jump Frame 2    Jump Frame 3

Thanks to Brian Schultheiss Which this script is modified from ( http://registry.gimp.org/node/20943 )