Luckily pamphlets written by the Diggers still exist, including The True Levellers Standard Advanced, and A Light Shinning in Buckinghamshire, so we know what they thought pretty well. As for what they did, essentially they tried to establish communes on common land, and where suppressed, there is a short overview with sources Here. The movement then shifted to less material objectives, and can be regarded as a forerunner of the Quakers.

But for me the interesting part of the question is how they (and similar groups especially among German Anabaptists) fit into the history of socialism. Firstly they are solidly on the anarchist flank of modern socialism, although the historic use of terms socialist, communist, and anarchist are overlapping and unclear (for instance Oscar Wilde refers to himself as a socialist, yet his views would today make him an anarchist). This could be contrasted with movements like the followers of Mazdak, who are more aligned with socialism as it is perceived today (being conducted by the state). The Diggers fit quite nicely into the category Christian Anarchism, along with Leo Tolstoy. This grouping can be summarised by: pacifism, egalitarianism, and opposition to the state and hierarchy.

There is to my knowledge there is no reason to believe first person to use the term anarchist in this context, Pierre-Joseph Proudhon (source definitely not take from wiki John M. Merriman, The Dynamite Club (2009), p. 42.), was aware of the Diggers or influenced by them, although his brand of anarchism (mutualism) differs significantly from the latter use of the term. Reading both The Conquest of Bread (regarded as the anarchist-communist manifesto, written by an atheist) and the Diggers pamphlets, I was struck by the similarity. Both refer to bread extensively, but much more importantly feature the idea of the earth as a common inheritance to all, as well as more general socialist principles and opposition to the state. I therefore think that the Diggers can be regarded as solidly within the anarchist communist school of thought, the main difference being the justification of this desired social order being derived from their theology, rather than material analysis or moral sentiment. Edit: a note on their theology, taken from The True Levellers Standard Advanced, the most striking thing to me was the belief that original sin (as in the book of Genesis), was the origin of hierarchy and the start of domination. I think this chimes well with leftist such as Murray Bookchin who effectively makes the same argument in secular terms in The Ecology of Freedom, and with the statement by Abdullah Öcalan that patriarchy (a form of domination) is humanities first great mistake.

Its also worth noting that the Diggers cited the bible extensively, so depending on the amount of historical credence you will allow the book of Acts (and accept their interpretation), they where merely applying a millennium old doctrine to modern circumstance.

As to whether they influenced the development of socialist thought historically, rather than simply where they fit into this history, it is hard to tell. Perhaps the ardent atheism of key "socialist" thinkers (e.g. Proudhon, Marx), would obscure their input historically, although in The Ecology of Freedom, Murray Bookchin clearly favours these kind of groups, and sees them as the ancestors of the modern left.

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