One can spot plenty of Scala-related projects using coursier in the wild. Here are a few of them.
scastie and scalafiddle
scastie and scalafiddle both use coursier to handle dependencies added by users.
Ammonite and mill
The Ammonite shell and the mill build tool both rely on coursier to handle dependencies.
Twitter's internal builds, based on Pants, rely on coursier to handle dependencies.
scalafmt and scalafix
The command-line interfaces of scalafmt and scalafix both rely on coursier for their installation.
Scala jupyter kernels
The scala Jupyter kernels Toree and almond (formerly jupyter-scala) both rely on coursier to handle dependencies.
Scala vscode language servers
The Visual Studio Code Scala language servers, metals, vscode-scala, and vscode-dotty, all rely on coursier to spawn their server process.
Other build tools
bazel-deps allows to handle Maven dependencies in bazel using coursier.
The fury build tool handles Maven dependencies via coursier.