If you love tinkering with your Mac, you can download the SanFrancisco font (direct link) and place the font files in your /Library/Fonts (that’s the Library folder at the top level of your Mac’s storage drive, not the one in your Users or System folder). Now log out and log back in to your Mac to activate the new font system-wide.

I recently installed SanFrancisco font as the default and I love it. I’ve also used other Yosemite font replacements like Fira, Source Sans, Input Sans, and even the old OS X Mavericks default, Lucida Grande.

You can patch any font you wish to be a system replacement font yourself. Unfortunately, it requires some geeky wet-work with the Terminal.

Though you can’t choose any font you wish, you can use these modified Fira Sans fonts to replace Mac OS X Yosemite’s default System Font. Best of all, it’s easy to do and involves absolutely no hacking of system files.

1. First, download Fira System Font Replacement.
2. Next, drop the fonts into your /Library/Fonts folder. Note that this is not your User Library folder, but the one you see at the root level of your storage drive.
3. Now simply relaunch the Finder. To do that, Option+Click the Finder icon in the Dock and choose “Relaunch” from the menu.

You should immediately see the new font appear in all your windows and menus. If you don’t like Fira Sans as the system font, you can simply remove the fonts from the Fonts folder and relaunch the Finder again.

As I stated at the start, this won’t work with just any font. This version of Fira Sans has been altered to supersede Apple’s default system font. The original system fonts haven’t been touched, which is why you can switch back simply by removing the Fira Sans.

These fonts are intended as a system font replacement on Mac OS X 10.10 Yosemite. They are based on the Fira Sans font family by Erik Spiekermann and Ralph du Carrois, and are licensed under the Open Font License version 1.1 or later. The System font replacement package has been prepared by Jens Kutilek.