A simple angle bracket for reinforcing furniture, shelving, or other stuff. Dimensions and hole spacing are customizable. You can also enable a second brace, but if so you may need to re-orient the model to print it without supports. For strength, I would suggest printing with 3 or more shells and a relatively high infill.
Revised customizer options for the triangular braces. Now you can enable each brace independently. Perhaps useful if you want to print a symmetrical pair.