That would be nostr:nprofile1qyv8wumn8ghj7mn0wdj8y6tkv5hxzurs9aex2mrp0yq3zamnwvaz7tmwdaehgu3wwa5kuef0qqsfxfs52ud0ewk569apj8hzs83ea6amgxunlty0mpuzjc32avgj7ng29zt4k !

It's also a play on the terminal command "mkdir" which stands for "make a new directory" (folder).

Alex explains the background of why he built MKStack inspired by MK's vibe coding projects in this podcast:

nostr:nevent1qvzqqqqqqypzql6h8a2asaww3mw99rklsg55nlf2h8uuvhv3ffqzy4nrkznf00s8qqs96kxmxc7mufgt6n2rxpphg8ptyx2kl47a7rj389jrwmvjy6rhuhg6z982s