It's an actively-developed, secure, professionally-usable distro that uses musl libc and doesn't have systemd. It's not super easy to configure as a desktop system, but it's very small and I like to keep it around for VMs and such.
While not super easy to configure, the base install + modify then choose to commit changes workflow is pretty cool. I can try all sorts and when I (immediately) get stuck just reboot and have another go.
One good example would be containers used for CI jobs, which get downloaded hundreds/thousands of times a day. They benefit from being based off as tiny an image as possible.
As far as I understand, most people use alpine in docker containers due to it's being quite lightweight with a decently large number of packages.
I personally use it directly on the hardware on my personal server and I love it. It's all the fun and flexibility of a minimal system like arch, with all the simplicity of upstart.
Also it takes about 2 minutes to install, which is helpful for setting up testing environments.
Same here (home server on bare metal). The simplicity, hardening and lack of unnecessary cruft means a much smaller attack surface than, say, Ubuntu. It reminds me of OpenBSD that way.
I used it as a base for docker containers, but depending on project Ive found that sometimes the lack of locale support is making it a non-viable option. I read there are ways to get it working, but I never did.
As others said its useful for containers and vms, but also other network equipment like firewalls and routers. Its easy to let it run completely in ram and offers a hardened linux kernel.
Alpine is very popular in the Docker community, due to the distro's minimal footprint. So I imagine at least some of the intrest may stem from those who create Docker images.
