Martin Heidegger
What is Being? We have forgotten the question.
Misconceptions
Heidegger is an existentialist, like Sartre.
He rejected that label. In the Letter on Humanism (1946), he writes that Sartre reverses the sentence of metaphysics ("existence precedes essence"), but that reversing a metaphysical sentence leaves it a metaphysical sentence; he adds that the basic tenet of "existentialism" has nothing in common with the sentence of Being and Time on the essence of Dasein. Sartre claimed Heidegger as his source. Heidegger called his project a fundamental ontology, not a humanism.
"The nothing nothings" is an absurd sentence, gibberish.
That is Carnap's charge (1932). Heidegger is aware of the objection: in the lecture itself he writes that logic seems to forbid the question of the nothing, then holds that the nothing is more original than negation. One may find his answer insufficient, but the sentence is not dropped without an argument. In the 1946 Letter he adds that thinking against "logic" does not mean defending the illogical. See the argument "Why is there something rather than nothing?".
For Heidegger, technology is evil and must be rejected.
He writes that what is dangerous is not technology, and that it has nothing demonic. In his view the danger is Enframing (Gestell), a way of seeing everything as a stock to be ordered, human beings included. But he also holds that treating it as neutral is impossible: it would be the worst way to be delivered over to it.
Being-toward-death means thinking about your death all the time, or about what happens afterwards.
Heidegger writes that dying is not an event but a phenomenon to be understood existentially. His analysis says nothing about what happens "after death": he writes that nothing is decided about that, and that it stays "this-worldly". He speaks of how one lives, knowing that death is a possibility that is always one's own.