Ziteboard
Platform: web-based, Chrome app/ext, Android app
Description: A zooming, interactive whiteboard (free for individual use, premium features include realtime collaboration); instantly begin without login, or create account (connects to Google) to save boards for later access; save as image or PDF; add images or upload PDFs as backgrounds on the board; includes shape recognizing for cleaner illustrations; to begin immediately, visit app.ziteboard.com
Common Strategies: have students demonstrate thinking (pro tip: record ziteboard sessions with Screencastify or other screencast app); organize ideas and brainstorm collaboratively (small groups, partners, or as a whole class); have student annotate PDFs by importing them and drawing overtop (can export as a PDF or image once done)