Gimp

Draw a circle

• Draw an elipse selection
• Select > To Path
• Pick a color
• Edit > Stroke Path

Layer fadeout

• In the Layers tab, you can directly change the percent transparency of any layer with a slider

Edge fadeout

• select the area to preserve; IF YOU WANT THE EDGE TO FADEOUT, SELECT A BOX JUST INSIDE THE ENTIRE IMAGE; YOU CAN ALSO USE THE MAGIC WAND TO SELECT AN AREA, AND SHRINK AND GROW AS NEEDED
• SELECT->FEATHER, GIVE IT ABOUT 5 PIXELS; THIS APPEARS TO DO NOTHING BUT PUT A BIT OF ROUNDED CORNERS ON YOUR SELECTION, WEIRD EH?
• INVERT THE SELECTION, AND HIT DELETE – vioala, GIMP FADES OUTWARD. YEs, IT’s weird!