Mediawiki: https://www.mediawiki.org/wiki/MediaWiki
Padlet: (tutorial) https://www.youtube.com/watch?v=UkBnwPqaIjA&feature=youtu.be Padlet is a virtual 'wall ' on which you and your students can place 'sticky notes' for group projects.
Blogger: a Google app (Other Google apps available at: https://www.lifewire.com/project-wikis-using-google-sites-771663)
WordPress: set up a free blog or website
(Article on Blogger vs. WordPress)