The best replacement for corners is box pleats.

The best alternatives to corners are rated as following:
★★★★★  box pleats
★★★  edges
★★★  square corners
★★★  caulk
★★  vertices
★  grout
★  hospital corners
  edges is

Your alternative for corners is not listed? Suggest!
Speaking about corners, one probably shouldn't forget about bias tape.

Other search terms related to corners and their ratings are:
★★★★★ bias tape
★★★★★ consent
★★★★ bias binding
★★★ bullnose
★★★ images css
blanket binding
You have in mind a companion for corners and it is not yet here? Propose!



Google Trends

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corners
box pleats
edges