The "single tax" was an idea of
Henry George, one of the major figures of
progressivism around the
turn of the century in the
United States. Basically, George thought that
taxes should be based on ownership of
land, which would take money out of the hands of
trusts and allow the
government to help people in
poverty.
Why? George argued that God gave mankind the Earth. Whoever takes ownership of a part of the Earth is denying the rest of mankind its right to that part of the Earth and the resources within, and so the owner should have to compensate others for taking something that wasn't theirs to begin with.
Tolstoy and Mark Twain were two of the most famous followers of the single tax movement, which peaked in the early 1900's and had a brief rebirth during the Great Depression. Today, the use of a single tax system is rather rare: Denmark, Alaska, and Alberta use variations on the idea, as do some cities in the US, Australia, and New Zealand. It continues to be advocated by the Council of Georgist Organizations (http://www.progress.org/cgo/) as a way to reduce economic inequality.