There isn't "an" alternative to PGP, because the idea of a single tool like PGP that covers all the use cases PGP attempts to cover has been revealed to be bankrupt. PGP does a bad job at practically everything it's applied to, because different problem domains ask different things from their cryptography. Backup tools want deduplication. Secure messaging wants relentless forward secrecy. Package signing systems want short, simple signatures --- meanwhile, messaging systems want authenticated key exchanges without signatures. Sometimes you want non-repudiation, but often you want the opposite.
To put this in perspective, it's a little like someone invented a bad balanced binary tree before anybody else came up with a hash table or a radix tree or a heap, and then a weird subculture formed around that balanced binary tree based on the idea that you should only ever use that tree algorithm, even though someone subsequently came up with red-black trees that were superior in every way to the original.
it's a little like someone invented a bad balanced binary tree
It's a little like that culturally but it's almost entirely unlike that technically - a suboptimal data structure or algo tend to be just suboptimal-but-functional whereas bad cryptography and bad cryptography engineering often fail catastrophically. I know you know this, of course! But for one thing, someone used an iffy analogy on the internet, etc. For another, PGP people love misusing exactly this sort of analogy.
I'd use the analogy of "someone came up with C and then people came up with high level languages and even low-level languages that provided memory safety and..." but then we'd just be in another debate about how mired in the 1980s we should remain. :)
To put this in perspective, it's a little like someone invented a bad balanced binary tree before anybody else came up with a hash table or a radix tree or a heap, and then a weird subculture formed around that balanced binary tree based on the idea that you should only ever use that tree algorithm, even though someone subsequently came up with red-black trees that were superior in every way to the original.