beamer-varboxes
A LaTeX package
The package
The GIF on the right showcases the effect of different settings.
beamer-varbox provides variable size corners for Beamer boxes. The current version is fairly simple and only has one option cornerpercent, which can be called either when importing the package or when setting the beamer template manually and set the scale of the corner relative to the standard corners of the rounded preset. The value 1 gives the standard corner from the predefined option rounded. The value 0 gives a sharp corner. The default value is 0.3.The GIF on the right showcases the effect of different settings.
If you want to check it out and try it for yourself, you can do so by updating your LaTeX distribution and then calling \usepackage{beamer-varbox} in your preamble. Alternatively, you can manually install it from the source Github.