Google Sites is the first option that comes to my mind when thinking of an alternative to Wikispaces. G Suite for Education users can create websites on Google Sites. Whoever creates the site can invite other G Suite users to add content to the site.
Weebly for Education is another option for collaboratively building a website. A free Weebly for Education account enables you to include up to 40 students in your account. You could have all students contribute to one site.
One more option to consider is using Edublogs with a template that is designed to feature static content more than blog posts. Then you can invite your students to contribute to the site. The nice thing about Edublogs, like Weebly for Education, is that you can administer your students' accounts.