I've created a whiteboard which I use every lesson when teaching maths, though it can be used for anything. It currently has a few hundred teachers using it daily. It's designed for use with touch-screen interactive whiteboards in classrooms, and stays in sync with your phone/tablet/whatever without signup/login.
You can also find me on Twitter where I post updates etc: https://twitter.com/jakegmaths
Some features and cool things:
* Sync devices without signup - offline by default, just hit 'sync devices' and use the same code on multiple devices to sync
* Touch-first - 1 finger draws; 2 finger pan/zoom; 3 finger gestures like changing pen colour
* Add images - when teaching, this is usually photos of student work taken on my phone and auto-sync'd to the whiteboard at the front of the room
* Add PDFs - when teaching, these are usually past paper exams which I then annotate over with the class
* Zen mode - 3 finger tap or hit the ∞ icon to hide the UI; something I use every lesson so students can focus on the actual maths (there's also a fullscreen button when not on iOS)
* Visualiser - often when teaching we'll work on paper with a webcam aka 'visualiser' pointing down at it; this projects that to the main whiteboard, with optional cropping, freeze-frame and snapshots
* Screencast - many teachers use eg PowerPoint to teach; instead, I'll use PowerPoint in edit/design mode rather than slideshow mode, with a locally-cast cropped portion of that on the main whiteboard at the front of the room. This enables me to eg edit my PowerPoint as I go and use all the PowerPoint tools not available in slideshow mode
* Instant replay - hit the play button to play back all the scribblings currently showing on the screen
* Magnet mode - when sync'd with another device, use the magnet icon so the other device follows you. Most of my teaching is now via a tablet-with-stylus anywhere in the room, and as I pan/zoom around with the tablet the main whiteboard comes with me... but only when I want it to by activating the magnet
* Student mini-whiteboards (MWBs) - if my students have devices and I want them to use them, I 'sync devices' then enable student MWBs and each student has a live copy of the whiteboard, and I can see what they write and can showcase any student instantly on the main board
* PWA support - install as a PWA and you can download whiteboards as .iwb files which can then be double-clicked to open/edit on desktop
* Free - I have no plans to charge for this
* The client is a single Show HN: Infinity Whiteboard, Designed for Teachers
mathsuniverse.com