Africa, bucking global trends, raised more VC dollars in 2022 than 2021. But its unicorn list stayed stagnant.

Mem, an AI-powered note-taking app, has raised capital from OpenAI's startup fund -- one of the first companies to do so.

For years, competition and cheap money led venture-capital firms to invest heavily in early-stage startups. But now, as VCs tighten their belts amid economic worries, some of those startups are facing a slowdown in funding and may have to show a clear pat...