These are resources, not necessarily recommendations (though for some tools I've written a glowing review). Some are free and others are free to try then require purchase. Please check them out and decide for yourself if they will work in your classroom.
Storybird: free trial then ~$5/month - students write stories based on images presented (from picture books to novels
Boomwriter: introducing various writing strategies and offers students space to practice their writing while incorporating those new techniques
Parlay - reading, writing, listening, watching, discussing in round-table format