The baseline of Reformed Druidism is that it functions like an open-source spirituality. The rituals and language in the RDNA are symbolic and are not necessarily meant to be interpreted literally, but you can if you want to. This way, participants interpret things in ways that are meaningful to themselves. It's more of a philosophy (with rituals and rites of passage) that have appealed to people of a wide range of existing beliefs. The RDNA is the oldest form of 20th century Neo-Druidry, but isn't necessarily Neo-Pagan.
NRDNA: New Reformed Druids of North America
Isaac Bonewits created the NRDNA in 1976 to appeal to neopagans. The NRDNA adapted a few influences from various pagan groups including Wicca among others. The NRDNA is still considered fully part of the RDNA; they kept the Two Basic Tenets of Belief, they kept the same organizational hierarchy, they kept the ordination lineage to the RDNA's founder David Fisher, and the clergy retained voting rights on the RDNA Council of Dalon Ap Landu. The NRDNA was Isaac Bonewits' first attempt at creating a worldwide pagan church. Previously in 1974 Isaac wanted to push legislation for the RDNA to declare itself an "Eclectic Reconstructionist Neopagan Priestcraft." Almost all the non-pagans in the Council vehemently disagreed, and a lengthy debate ensued. The result was the formation of the NRDNA which still has active Groves and Protogroves today.
SDNA: Schismatic Reformed Druids of North America
When Isaac created the NRDNA, he was also developing the exclusively neopagan SDNA: The Schismatic Druids of North America. In this offshoot, Isaac kept the customs and rituals of the RDNA & NRDNA, but detached from the Council of Dalon AP Landu entirely, permitting him to pass any legislation he wanted. He created new bylaws for Groves to regularly report to the SDNA Mother Grove or be deemed inactive. Above all, anyone who desired to become SDNA clergy had to declare themselves neopagans or he wouldn’t ordain them. All SDNA clergy still required an ordination lineage back to David Fisher of the RDNA. The small handful of SDNA Groves fell apart and dissolved by the early 1980s. Isaac took inspiration from the SDNA and re-emerged with ADF in 1983 which is in fact a growing global neopagan church, but has zero formal connection to the RDNA. There are currently no active SDNA Groves, which means whoever creates the next one gets to be the new SDNA Mother Grove, with all due authority. You would just need to find an RDNA or NRDNA clergy to ordain you.
HDNA: Hasidic Druids of North America
The Hasidic Druids of North America was co-developed by Isaac and others who were looking for a syncretic hybrid neopagan offshoot of Schismatic Druidism for people of Jewish descent. They added so many laws and restrictions to the HDNA that it became difficult to view the group as a branch of Reformed Druidism. Arch Grove may have been the only known HDNA Grove, but it is no longer active.
ZDNA: Zen Druids of North America
There was only one Grove (Evergreen) that incorporated Zen philosophy with Reformed Druidism to the point that they created a whole offshoot. Evergreen Grove was eventually absorbed into Emerald Grove in 1997 and is now regarded as an RDNA Grove. Zen Druids likely take much inspiration from Alan Watts.
EDNA: Egalitarian Druids of North America
There have only been one or two EDNA groups as far as we can tell, and they've only ever been Protogroves since they don't believe in the practice of ordinations to the First Order, Second Order, or Third Order. This means an EDNA protogrove is run by a group of individuals who regard each member on equal bearing.
o.d.m.: order of druids minor
Deliberately lowercase, the order of druids minor is for the most part classic RDNA but with the added principles of Humility, Humanity, & Observance. It incorporates a few philosophical ideas espoused by Marcus Aurelius, Pelagius, and St. Francis of Assisi. It is definitely a more overtly contemplative branch of the Reform.
RDEM: Reformed Druids of the Earth-Mother
The Reformed Druids of the Earth-Mother is basic Reformed Druidism but for those beyond the North American continent.
RDW & MOCC: Reformed Druidic Wicca & Missionary Order of the Celtic Cross
Reformed Druidic Wicca was founded as a branch of the RDNA in 1983 as a hybridization of Reformed Druidism and eclectic Wicca. Around 1994-1996 the name was changed to Missionary Order of the Celtic Cross (MOCC). The members of MOCC are also a very diverse amalgam; a good portion identifes as Celtic Pagan by varying terminology, another portion identifes as Christian. With the parent group being located in Oklahoma, some MOCC members also practice their Cherokee spirituality. Buddhist, Hindu, and several other world religion practitioners also make up the demographics. Overall, MOCC is adept at embracing diversity and religious pluralism, though this branch is geared toward those who do believe in a supernatural higher power.