This list will focus on the Teaching of Gurdjieff. There are a very many lists and sites on the web which purport to discuss this area but in fact present mostly deviations, distortions, or worse, egoistic and pseudo-intellectual pontifications where the "empty is poured into the void". This list might approach this teaching not as a "System" or "school of thought" or "philosophy" or "psychology of types" or a "place where one can hone one's debating skills", that is, as some sort of hobby which provides ready made answers and titillation but rather as a tradition or sacred spiritual discipline whereby one might discover and deepen one's essential search and real questions.
Those who are relatively unfamiliar with these ideas are welcome as are those with experience. A good book for those not familiar with these ideas is "In Search of the Miraculous. Fragments of an Unknown Teaching" by P.D. Ouspensky.
The general aim of the Work might be said to be threefold- "To awaken", then "to die", then "to be born".
Since the first aim is "to awaken", this Teaching tells us that we are currently asleep (or trapped in a prison or hypnotized to believe we are much more wonderful and significant than what we actually are). But this too must be verified in oneself and not accepted as a matter of "faith".
To begin to get glimpses of oneself as one truly is and not as one imagines oneself to be is clearly difficult and unpleasant. One often does not like what one sees. Furthermore, there seems a great resistance to efforts to "know thyself". One must be able to bear the inevitable necessary suffering which results from the realization that one does not know oneself, that much of one's life has been lived under illusion and in a dream-like state of sleep.