You could have downloaded WriteTyper 2.0 for Mac from our software library for free. This free software for Mac OS X was originally produced by Urinx.
From the developer:
WriteTyper is an open source application that allows you to change your keyboard sound. It can make old typewriter sounds when you keypress, let you more enjoy the time of coding or writing.
Notice: for it to work, Accessibility for WriteTyper must be enabled.