1: StackOverflow
2: ChatGPT
Nothing else comes close. Certainly not any new language.
WHY these two things are the biggest developments in programming is because they help developers solve problems and learn new things from a global accumulation of programmer knowledge.
If there was a Nobel Prize for computing then both StackOverflow and ChatGPT would be deserving of it, or the people behind them anyway.
I am actually super interested and positive about Mojo but I can't take the title seriously. Not even close. As is, it is basically a yet another new (completely distinct language from Python) that looks and feels kind of like Python and hopes to convert a bunch of users, but is not really Python, and embeds CPython in the same way that Swift (4TF) could already do (and a lot of random software also do to use Python as their scripting engine.)
GitHub?
The cloud?
GPUs? Multi core CPUs?
Subscription models?
SPAs? Ajax?
VC funding?
Mobile phones?
I don't think you appreciate what has happened over the last several decades. I'm sure I'm missing a ton of things as well. Stack, overflow and chat GPT probably wouldn't even make my top five list over the last 3 decades. If you look 3 decades out, I'm sure there will be some AI stuff in there, but it is not even close to making the list right now IMO.
And stackoverflow is number 1 :)
An incremental improvement with an enormous impact.
4. React
5. Rust