This work offers an introductory overview of Metamonism (Processual Ontodynamics) through the lens of key 20th-century philosophical schools. The text is structured in three thematic blocks: (I) criteria of reality, language, and meaning (pragmatism, logical positivism, analytic philosophy); (II) subject, perception, and understanding (phenomenology, existentialism, hermeneutics); (III) social, linguistic, and power structures (critical theory, structuralism, poststructuralism, neo-Marxism). It is shown that 20th-century philosophical thought, despite its diversity, moved toward the rejection of static substance in favor of processuality, difference, and action. Metamonism offers a unified axiomatic foundation in which these intuitions acquire a rigorous deductive form. The sole invariant of the system is the Prohibition of Indifference: absolute identity (I, I) is excluded from the domain of the actualization operator Dom(P) = {(D, I) | D ≠ I}. From this invariant, the entire subsequent dynamics of reality is deduced — from the emergence of space and time to consciousness and complex structures. The motto of the work — "Ex uno omnia" ("From one, everything") — symbolizes the overcoming of the fragmentation of philosophical knowledge. The work contains a methodological note and references to published preprints of the series "Metamonism (Ex uno omnia)." ( direct link )