"Miao Unicode" is an open source, Graphite-enabled font for the Miao (Pollard) script used by several language communities in southern China.
The documentation page can be found at http://phjamr.github.io/miao.html.
The Miao script was added to Unicode in January 2012 with version 6.1.0. "Miao Unicode" appears to be the first publicly available font which covers this Unicode block.
Adobe's open source font "Source Sans Pro" provides the Latin script counterpart for the font and the base for the Miao design.
Since the Miao script involves complex rendering (such as vowel marks being raised/lowered according to the tone) the font will only behave correctly in applications which provide Graphite support. These include Mozilla Firefox (11+), LibreOffice (3.4+), OpenOffice (3.2+), Xetex (0.997+). For more information see http://graphite.sil.org/.
The Lisu (Fraser) script, also used in southern China and neighbouring areas, is included in this font as it may be helpful to have a matching design. Lisu is already supported by other fonts, including the Noto project.