You can now create reusable actions using shell scripts and even mix multiple shell languages in the same action. You probably have a lot of shell script to automate many tasks, now you can easily turn them into an action and reuse them for different workflows. Sometimes it's easier to just write a shell script than JavaScript or Docker. Now you don't have to worry about wrapping it up your scripts in a Docker containers.

Here's an example of how you can use composite run steps actions:

workflow.yml:

jobs:
  build:
    runs-on: windows-latest
    steps:
    - uses: actions/checkout@v2
    - uses: octocat/say-hello@v1
      with: 
        name: OctoCat

octocat/say-hello/action.yml:

inputs:
  name: 
    description: 'Your name'
    default: 'No name provided'
runs:
  using: "composite"
  steps: 
    - run: echo Hello ${{ inputs.name }}.
      shell: bash
    - run: echo "Nice to meet you!"
      shell: pwsh

Learn more about composite run steps and visit the GitHub Actions community forum for questions.