Their functions are also limited to triggers relating only to Netlify events

to be clear the functions are also exposed to the public internet as http endpoints so you can ping them from anywhere else, including, for example, your frontend app, or Zapier [1], or GitHub Actions or cron service of your choice

(i work at netlify)

1: https://www.netlify.com/blog/2018/11/07/automate-your-netlif...