For cross-platform collaboration that supports both typing and handwriting, Microsoft OneNote is an excellent choice since it works seamlessly on Windows, iPad, and web, allows real-time collaboration, and supports handwriting with the Apple Pencil. If your group prefers stronger handwriting features, Notability on iPad paired with its web version can work well, though it’s more limited for Windows users. For a simpler option focused on quick sketches and brainstorming, Google Jamboard offers an easy web-based whiteboard. Overall, OneNote is the most reliable and versatile option for your project.