Judaism and Samaritanism (which many may classify as a sub-form of Judaism)
@note on Karaism - this is a hard to define group.
Some consider themselves separate, others recognise themselves as part of the Jewish nation.
Likewise from the other side - in some places "rabinic" (or "normative") Jews saw the Karaites as part of the whole, in others, the "rabinic" Jews regarded the Karaites as "other".
Also - only a sub-segment of Karaites are "purposeful" Karaites - a philosophical movement, while others are "ignorant" Karaites - a Jewish group with less access to the rabinic legislative tradition.
From the side of the evil ones -
the Nazis killed Karaites as Jews.
@Islam -- Islam does not follow "Old Testament" (ie: Hebrew Bible). They follow the Koran and Hadits - many of the stories in these parallel the Hebrew Bible - but it is a wholy different book.
...if we want to talk "micro groups"
- There are the Bnei Menashe in India/Burma - they consider themselves part of the Jewish people but they nevertheless undergo a formal Orthodox conversion -- thus, the technical Jewish view that they agree with is that they are a separate group that is trying to re-blend.
- the Abayudah in Ugandah.
They started keeping Judaism on their own in the 50ies and have been seeking Jews to convert them to "proper" Judaism. Conversions are currently ongoing.
- there is a similar group of Indians in Peru
- the Subotniks of Russia - Russians who rejected Russian Orthodox Christianity in the 18th century. There are actualy some subgroups:
- the "Gers" - like the Abayudah - they sought full conversion to Judaism but were kept separate from Jews by force under the Tzar. Rabbis snuck over when they could to convert people and teach.
- Karaite Subbotniks - they try to follow the "written Torah" only - based on their own interpretation - and they enjoy arguing with "normative" Jews. Before WWII, they tried to keep contact with the Karaites of Russia and used prayer books from them.
- Christian Subbotniks - kinda like Seventh Day adventsts