https://en.wikipedia.org/wiki/Henry_GeorgeIt's idea of a usage tax on the untransformed value of land as a replacement for income tax.
For Henry George here are the good points:
1. At least people are valued so it is better than socialism which has shown a trenchant disregard for the individual and the product of her or his labor when applied in reality. He correctly predicted that if Marxism was applied that it would lead to dictatorship.
2. It comes from the point of view that income tax is a disincentive to work.
It had many adherents across the political spectrum. He also personally advocated complete municipalization of public services. It had many supporters in the 19th and into the first few decades of the 20th century. George Bernard Shaw, Martin Luther King Jr, and center-left economic hero Joseph Stiglitz are among his many supporters.
Sometimes, in discussions in libertarian circles we see a Georgist stick his head up to say how his views are worth considering again.
I think the idea of one group unilaterally deciding the untransformed value of land is a onerous task that is suspect in how it could determine said value when the value could be entirely subjective depending on who would purchase it. It would likely require some all-knowing land management bureaucracy that would audit the land regularly. It would be very difficult in many cases to know what the original untransformed value of the land post facto. Arbitrary and subject to political influence.
As a libertarian, Georgism is problematic because of all the private property implications that are missing. Thus we are likely to see the tragedy of the commons, information gaps, and the economic calculation issue that can be arise if the land is considered commonly held and various municipal services are provided free by the single source as decided by town leadership or democratic means without competition from the market.
Without George though, we would not have had the game, Monopoly - as the Wikipedia article describes.