Inworld seems like a pretty cool site for both teachers and students.
You can create chatbots (that have audio and text ability, though I was having difficulty with the audio feature), and interact with ones that others have created.
There’s already at least one on the site that ELL students can access to practice English.
Students, and teachers, can also use it to create chatbots simulating historical characters.
It’s “freemium,” and you can certainly do a free project without paying.
I’m adding it to The Best Online “Chatbots” For Practicing English, as well as to The Best Places To Read & Write “Choose Your Own Adventure” Stories.
You might also be interested in The Best Tools For Creating Chatbots.