Moss requires little maintenance, is visually attractive, stays green throughout the winter and is soft on your feet. You can propagate moss to trees, planters and other surfaces by making a moss "milkshake".
Household weblog Apartment Therapy gives the following recipe for a moss growing "milkshake": Add two cups of water and two cups of buttermilk to a blender and top with a section of existing moss; this moss can be live or dead. Blend until you have a milkshake consistency, and use a paintbrush to spread the milkshake on whatever surface you wish to grow moss.
You'll need to use a mister to keep the moss moist for the first few weeks and keep in mind that moss generally thrives in shady areas. Using this method you can even get creative and draw pictures or write out short phrases in moss.
How to Grow Your Own Moss [Apartment Therapy]