Are there any Jewish sects which regard the Oral Law, Talmud and other interpretations of Tanach as unlawful addition to the religion? If yes who are they and what are their beliefs?
Currently, there exists a small Karaite community which claims to follow only the written law from teh tanach. On a website purporting to represent them, they give a history which lists other sects which, over history, have mirrored their beliefs (including "Sadducees, Boethusians, Ananites").
It is important to note two other points, though. One is the claim that, institutionally, Karaites and other seemingly strict-text groups have incorporated the practices, understandings and traditions of other groups. See here. The other comes only anecdotally from my conversations with Karaites over the years. They say that they DO have an oral law, but one that is local to each community. When the tanach text refers to unwritten laws of ritual slaughter, the Karaite wise man of each village institutes, based on his own understanding, what those laws are. There is no over-arching sectarian definition of the traditions and unwritten rules, but they exist, group by group.
The Rambam discusses this, and is very severe about someone who does so from his own ideas (in contrast to a child who was raised this way):