They all agree on collectivism, anti-capitalism, a commitment to violence, hatred of democracy, conspiracy theorising, Manichean world-views (not just about Jews) and so on.
However, it is Jew-hatred that is the prime locus of alignment – and has been since the 1960s (if not well before).
Then again, this hatred of the Jews from Leftists, Nazis and Islamists also ties in to their embracing anti-capitalism and collectivism. After all Marx himself (yes, a Jew) made a fatal connection between Jews and capitalism (in 1848 and as late as Das Kapital). Then Nazis did something similar between Jews and Communism. Nowadays, it depends on the time of day: sometimes “all Jews are capitalists”; other times “all Jews are communists”. It doesn't matter – whatever works against Jews GOES. I've even heard “auxiliary hypotheses” (Popper) as to why many Jews are centrists or apolitical (to “hoodwink people”, to “play both sides”, etc.).