Blaze predates Buck but Buck was open-sourced before Bazel. The two tools also have different origins (Blaze for server applications and Buck for mobile when I was at each respective company).

Buck was started after former google employees at facebook wanted to use something like blaze (ended up being called bazel). Kinda like a lot of other things they copied from google at facebook. Dremel -> presto, etc.

Groovy rules side-by-side:

https://buckbuild.com/rule/groovy_library.html

https://github.com/bazelbuild/rules_groovy#basic-example

As others have mentioned, Buck was open-sourced before Bazel but obviously inspired by Blaze.

There's also Please, which we wrote as a Buck replacement before Bazel was open sourced: https://github.com/thought-machine/please

(disclaimer: I wrote most of it...)

Pants is also a popular build system (started by an ex-googler?).