Bitcoin: nope [0]. Bittorrent: there's a huge ecosystems of clients written by different teams of people. Spark: do you mean Apache Spark? It has many contributors [1]. Tarsnap: is convenient plumbing wiring up S3 and the academic cryptography literature, neither of which are solo efforts. PGP: its most important manifestation is probably GnuPG, which also has several contributors [2]. Minecraft: Mojang has 47 employees [3]. I doubt Notch is the only person with code in Minecraft.
You do have a point that solo brilliant engineers can start projects that go on to have massive impact (cough Linus Torvalds), but once those projects have reach, they tend to have teams.
But initial implementations are a single person, and yes, once they have greater adoption do grow... that said, there's still a lot to be impressed by in initial release.
The most recent one that comes to mind are redux + redux dev tools. Though definitely have grown since initial implementation, it was one of the more impressive things I've seen recently. Second in my mind is git itself.