Aluminum Extrusion Double Corner Brace Support (for 20x20) : ID 1259 : $1.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Amazon.com: YAPIKAN 30-Pack Plastic L Bracket White 1 x 1 inch - Reinforced Plastic L Brackets for Braces - Small Right Angle Corner Support Brace for Wood Furniture Cabinet Drawer Chair Bookcase
Amazon.com: 4-piece Bed Corner Support,9" Corner Brace Bracket,Corner Brace Desk Edge, Box,Shelf Support for Wooden Beams,Metal Triangle Corner Support Fastener,Corner Bed Support Thickness 2.5mm Max Load 266lb : Tools & Home Improvement
5pcs Angle Bracket Metal 128x75mm Corner Brace Fastener Support w Screws - Black - 5" x 3" x 0.8"(L*W*H) - Bed Bath & Beyond - 28766945
Pergola Corner Brace Bracket for 4x4 Wood Posts (45 Degree Angled Support Bracket) - Walmart.com
Stainless Steel Fixing Plate Brackets Joint Fastener/Heavy Duty Shelf Bracket Corner Brace Support Wall Hanging-Pack of 4 - AliExpress
Independence Hidden Corner Bracket | Federal Brace