A huge part of usability is readability. So it's obvious to me that how fonts are displayed on-screen is an important component of software usability - both for traditional "proprietary" programs and open source software.
Imagine my excitement when I read about Google's Open Source Blog announcement of the improved "CFF" font engine, used for rendering on a variety of platforms including Android, Chrome OS, Linux, iOS, and many versions of Unix. Compact Font Format (CFF) is a descendant of the PostScript font format developed by Adobe. The FreeType open source software displays fonts, and the new Adobe CFF engine brings high quality font display to FreeType.
Check out the samples on the Google blog to see comparisons with the new Adobe CFF display. The new CFF produces more even blackness of text, fewer "smudges" or "blobs" within the text, more even and consistent character heights, and fewer "dropouts."
I'm looking forward to seeing this used in open source software projects, to improve open source software usability.