Traditions within Wicca, witchcraft and paganism and Systems within the world of High Magic can be likened to sects of Christianity. Each Tradition or System is alike in some core understandings, but vary widely in their beliefs, structures, and methods of operation. Some are so different that only vague similarities can be gleaned.
When one chooses to work in a coven, lodge or temple atmosphere, they adhere to the practices of their tradition but there are many practitioners who choose to work solitary within the guidelines of a specific Tradition or System. Whether the Tradition or System recognizes solitary practice as valid is wholly dependant upon the structure of that Tradition or System.
Within Wicca itself there are literally hundreds of Traditions, just as there are hundreds of Systems within Ceremonial or High Magic some claim a lineage of thousands of years, others hundreds, while still others are recent incarnations created by practitioners who have left other Traditions or have established a method of practice and belief systems so variant from established Traditions that they branch out on their own. Whether these new traditions are valid or not, I will leave to the individual, however I do have something to say on the creation of a "Tradition" of witchcraft or Wicca.
I recently read a post online in which the writer stated "I looked in books for a tradition I liked, but when I didn't find one, I created one of my own. I have always practiced solitary." In my opinion, what this person has created is their own system of personal practice, not a tradition. A tradition implies a method of doing something that has been handed down, established through a length of time. Should this person continue study and to practice in the same way, then pass their knowledge to another, it could be argued that they have created a tradition, but at this time, they have not.
The validity of a Tradition or System is determined by the integrity, honesty and scholarship of its practitioners and whether or not the teachings of the Tradition or System actually work. With that, I leave you to browse the list of Traditions and Systems by letter or to search: