Bamboo Point Turner & Presser. The best tool for creating the sharpest corners & for "pressing" seams by hand. Also, use round end to temporarily "mark" fabric with a crease.
Check out Linda's Sew Confident course for more tips on Perfect Corners!
As featured in Linda's Craftsy class Sewing Notions Workshop: Solutions for Savvy Sewing and Sewing with Silks.