Looks like excalidraw.com is an SSL error, but www.excalidraw.com works great. It's possible the github pages config could be changed to make both work, but this seemed easier to fix.
@@ -7,7 +7,7 @@
## Try it now
-Go to https://excalidraw.com to start sketching
+Go to https://www.excalidraw.com to start sketching
## Testimonials
Ben Kraft