CastDonut adds an inobtrusive circular castbar and global cooldownbar aroudn the mousecursor. Specially useful and written for clickcasting healers using Clique or similar addons.
Screenshot shows the castbar, imagine the cursor in it
You can edit some of the settings radius, thickness, color etc at the top of the cast.lua file.
There is a smaller donut inside the CastDonut indicating your global cooldown