One day when I was drawing an icon presenting 'tooth' at work, I opened pen tool and quickly add few points. Then I suddenly realized that I had to adjust all points manually while keeping the whole shape symmentrical. PAAAIN! What about drawing half of it and copy-and-flip it? I did, and the result was awful cuz I couldn't foresee the whole shape when I could only adjust half of it. PAAAIN!

So I build this little tool to help me simultaneously mirroring the parts I draw, then I can easily adjust the half shape to view what it'll become. It turns out that it's not just me who find this painful, hopefully it'll help many designers😜.