A few people were asking for this a while ago, so here it is, a (very) basic slopemap generator. It takes in height.bmp and spits out slope.bmp.
The red channel is the height difference in the x direction, green is in y, and blue is the average of red and green.
If absolute is checked, the absolute difference is given. 0 means no difference, 255 means 255 difference, up or down.
If it is unchecked, a colour of 128 represents a difference of 0, 0 is a difference of -255, and 255 is a difference of 255.
A better version will be put out, with more options and stuff, but this will do for now.
Image used
Absolute Difference
Relative Difference