Buddhadasa: the Birth of Modernism
Ajahn Buddhadhasa Bhikkhu was a 20th century Thai monk (1906-1993) who was the forerunner, indeed the founder, of Buddhist Modernism. Now before you start quoting David McMahan and insisting that Buddhist Modernism was invented by Western colonialists who invaded Asia, stole Asian culture and anglicized it, or that it was merely a reaction to Western colonialism—STOP. Asian Buddhists modernized their own religion for their own reasons, and not just as a reaction to Western colonialism. The problem with McMahan’s thesis is that, although he mentions an indigenous Asian form of Modernism, he only expounds on Western contributions to Modernism. Thus when Westerners examine Asian Buddhist history, all they see is their own reflection, their own Western imprint, which is another form of Orientalism. Students of Buddhist Modernism fail to see that it was a process that began within Asian Buddhism itself. Buddhadasa along with Dr. B. R. Ambedkar and Anagarika Dharmapala were all Asian Buddhists who proposed Modernist forms of the Dhamma.
Buddhist Modernism
Buddhadasa published a treasury of essays on the dhamma that bear the hallmarks of everything that we now call ‘Buddhist Modernism.’ The publishing of his lectures amounts to 50 volumes, the largest output from a single Theravada teacher, exceeding Buddhaghosa. Today we think of Stephen Batchelor as the founder of secular Buddhism, who insisted on a return to the original Pali scriptures and the earliest teachings of the Buddhists; made patticcasmnupadda the pivotal doctrine of awakening; got rid of ritual excess, magic and merit-making; taught lay people to meditate; rejected karma-as-rebirth; connected the dhamma with scientific empiricism; aligned Buddhism with the secular or the life of “this world”. No, in fact, Buddhadasa originated all of that before Stephen Batchelor was even born. Buddhadasa plumbed the depths of the Pali and Mahayana scriptures to tease out the teachings that would form the basis of Buddhist Modernism today. And Buddhadasa accomplished this with a clarity and genius for scriptural scholarship that contemporaries like Stephen Batchelor and John Peacock could not match. That is not to slight Batchelor and Peacock, whose work I admire, but to say that the foundations for Buddhist Modernism do not lie in ‘Protestant’ Westernism, but in Asian Buddhism itself.
The most complete library of Buddhadasa’s shorter works are available as free PDFs here (it’s a safe download):
http://www.bia.or.th/en/index.php/buddhadasa-media/books-texts/ebooks/pdf/category/3-books-texts
Santikaro is one of Buddhadasa’s foremost students who has translated much of his work. Santikaro has a new book, Under the Bodhi Tree (2017 Wisdom Publications), which lays out Buddhadasa’s teachings on patticcasmnupadda, non-self, karma and rebirth. But you could also read Buddhadasa’s “Kamma in Buddhism”, “Concerning Birth” and “Nibbana for everone” and you would get the same clear teaching, based on the Pali, that rejects karma-as-rebirth and shows that nibbana is realizable by ordinary people in this one lifetime. You can hear Santikaro’s teachings on Buddhadasa here:
http://audiodharma.org/teacher/129/
Buddhist Socialism
Buddhadasa was also one of the earliest proponents of engaged Buddhism. He wrote several essays specifically on Buddhist Socialism, including “Dhammic Socialism”(1967) and “Democratic Socialism”:
His socialism was firstly, based primarily on Pali scriptures and not on Marxism, but moreover it was an ecological socialism, based on the science of evolution and the doctrine of patticcasmnupadda, the interdependence of all life. This was at least 40 years before the notion of ecological marxism/socialism was even broached in the West as a possible ideology. (See Buddhadasa Bhikkhu and Dhammic Socialism by Tavivat Puntagavivat).
From “A Socialism Capable of Benefitting the World”: 
Dr. B. R. Ambedkar’s essay, “Buddha or Karl Marx?” sounds like an echo of Buddhadasa’s earlier teaching. Indeed, where Ambedkar was a master of engaged Buddhist practice, it was Buddhadasa who was a master of the dhamma of engaged Buddhism, who expounded the Pali scriptures that support engaged Buddhism. Putting Buddhadasa’s dhamma teaching together with Ambedkar’s activist practice yields a complete foundation for the path of engaged Buddhism.
In his essay, “A Dictatorial Dhammic Socialism”, Buddhadasa founds Buddhism socialism on the dhammaraja, a form of dharmic monarchial government found in both Pali and Mahayana scriptures. Buddhadasa critiqued Western democracy and freedom as too ego-centric and selfish, promoting excessive individualism. He proposes interdependence as a natural ‘limit to freedom’, but as promoting conditions that support flourishing for humans and all species collectively.
Buddhadasa’s other well-known work on Buddhist Socialism is ” A Socialism Capable of Benefitting the World”. In this essay he softens the stance of “Dictatorial Dhammic Socialism” and contrasts the ethics of Buddhist socialism with the violent repression of mid-century communism. I do not espouse Buddhadasa’s “dictatorial” politics, which reflects the tensions and limits of mid-century socialism. Nor do I minimize the repressive effects of this form of authoritarianism. Rather, I would bring Buddhadasa’s dhammic socialism up to date by pairing it with a Commons-based theory of cooperative socialism, a 21st century invention.
No Religion
And finally, Buddhadasa was not a Buddhist fundamentalist, but a pluralist who thought that Buddhists should support whatever is “dhamma” in any religion. He did not see the necessity of practicing Buddhism as a religion at all. Rather, he said the dhamma is beyond dogma and rituals of practice, and wrote an essay on the subject call “No Religion.”
Please try to understand this correctly. When the final level is reached, when the ultimate is known, not even man exists. There is only nature, only Dhamma. This reality can’t be considered to be any particular thing; it can’t be Thai, Chinese, Indian, Arab or European. It can’t be black, brown, yellow, red, or white. It can’t be eastern or western, southern or northern. Nor can it be Buddhist, Christian, Islamic, or anything else. So please try to reach this Dhamma, for then you will have reached the heart of all religions and of all things, and finally come to the complete cessation of suffering.
Engage! 
I went on a retreat with Santikaro and he told us a lot about his time with Buddhadasa. It was a good experience
I’m interested in Santikaro’s teachings as well. Checking out his talks on audiodharma. http://audiodharma.org/teacher/129/ He has left monastic life in Thailand and lives at Liberation Park in Wisconsin with his wife.
yes. he comes down to Kansas City to lead weekend retreats once a year,
http://www.rimecenter.org/?p=1228