I actually contributed to Excalidraw, it’s a great project! They also use my ink (MIT licensed perfect-freehand library) for their pen tool. While tldraw mostly grew out of another project of mine (globs.design), I took a lot of inspiration from Excalidraw’s feature set. We’ve since caught up with eachother on a bunch of features (sticky notes, labels) and hopefully will continue to trade tips and features as separate open source projects.