Ask HN: What are some long foretold/delayed technologies that now exist?

Cold fusion and quantum computing have long seemed just on the cusp of realization, and have been promised as game changers, but practical application always seems to be at least ten years out. What are some examples of other important technologies that seemed to be similarly elusive over the last 50 years but now exist in a cost effective/practical form? It’s okay if they’re obscure.