As Pieter van der Wilt said in comments:
Well nothing really very outstanding. The great achievements of mankind during the last 200 years come mainly from highly industrialized nations (UK, France, Germany, USA, etc…). Greece is a small country with a fairly high level of creativity.
All nations are great, because humanity is great. The literature and music of Modern Greece have unparalleled depth and diversity and lyricism, and are a gift to the world. (Though that is just as true of the literature and music of Georgia, and Kyrgyzstan, and Bolivia, and Vanuatu.)
As Pieter said in his answer, Byzantium preserved ancient Greek scholarship—but didn’t build on it: that was left for the Western Renaissance. I could add Orthodox Christianity; but as theology rather than ritual, all the work had been done by 800 AD anyway.
If you’re after technological achievements, well, there are individual Greeks who have done things; overwhelmingly and inevitably, they’ve done things in the UK and the US.
We’ve made much more of a recent impact on our immediate region of the Balkans, as anyone in the region will tell you. But you spoke of the world, not of our neighbourhood.
From your comments to Pieter, OP, it looks like you’re reaching at a comparison with the Muslim world. But the game now in advances for humanity is a globalised game. The Ummah doesn’t get its own Golden Age any more; we’re much too interlinked for that. The Ummah gets to contribute to the advances for humanity, by taking part in the research and the stewardship spearheaded (for now) by the West. The West will likely yield its mantle within our lifetimes to China. The part of the Ummah that has relied on oil will have to work out what to do once oil no longer matters—and how to work with the West and China on the cleanup.
And I should hope that over a billion Muslims don’t need to draw lessons by comparison with a small bankrupt country of 10 million.