Free tools related to digital communication are plentiful and constantly changing. The list of tools on this page could never be complete.
One good thing to keep in mind about creating digital content is that a quick Internet search will often be very helpful as you work to figure out how to manipulate your digital work in some way so that it is represented the way you want it represented on your website: How to change that PDF into an image file; how to embed that audio clip; how to upload a screenshot; etc.
Still, some of the tools listed below might be useful. Have fun!
Google Suite
Google Docs, Google Drawing, Google Forms, Google Sheets, Google Drawings, Google Sites, YouTube, Gmail... Google offers several very useful tools that will help you and students add content to digital portfolios.