The main idea of "Socialism: Utopian and Scientific" (1880) was distinguishing scientific socialism and utopian socialism. Engels begins by chronicaling the thought of utopian socialists, starting with Saint-Simon. He then proceeds to Fourier and Robert Owen. In chapter two, he summarizes dialectics, and then chronicles the thought from the ancient Greeks to Hegel. Chapter three summarizes dialectics in relation to economic and social struggles, essentially echoing the words of Marx.
(Introduction by Wikipedia)