What are some open source projects that had substantial initial releases or updates that seemingly came out of nowhere?

With a lot of open source projects being worked on largely out of passion rather than financial gain I feel like there must have been several times where a release caught people off guard and "came out of nowhere" with its impressive scale.

To give some examples of how this might happen maybe it was an initial release dropped to the public in a complete state that had been worked on for a while privately or a project that was dormant for an extended period of time and picked back up.

Can anyone here think of an example? It doesn't necessarily need to be something groundbreaking maybe it got people excited in a very specific niche.

If you do have an answer I'd appreciate it if you could elaborate on it.