The last three evenings I've spent building two new command line tools:
miles (Mirror Tiles)
jiles (Join Tiles)
The purpose of the tools is to speed up and ease the task of creating tilesheets for my characters. I can draw all animations for a character facing right in a tilesheet, then I can use miles to create a copy of the sheet but with the individual tiles horizontally flipped. And with jiles I can join multiple sheets e.g. all sheets found in a directory into one big sheet of tiles. Hopefully this will remove some of the more tedious tasks related to tilesheets.
For anyone interested I've shared the code for these tools on BitBucket:
Feel free to use the code in whatever way you like.