Patents
Microsoft has several patents in the United States on subpixel rendering technology for text rendering on RGB Stripe layouts. This had caused FreeType, the library used by most current software on the X Window System, to disable this functionality by default. Since May 2010, the patents US5155805, US5159668 and US5325479 have expired worldwide and thus FreeType has its bytecode interpreter enabled by default.
Apple was able to use it in Mac OS X due to a patent cross-licensing agreement.
The patents 6,219,025, 6,239,783, 6,307,566, 6,225,973, 6,243,070, 6,393,145, 6,421,054, 6,282,327, 6,624,828 were filed between 1998-10-07 and 1999-10-07, thus should expire in 2019-10-07.
Read more about this topic: Subpixel Rendering