Brush Ninja is a super simple, no-download, no-signup animation tool. It is 100% unblocked on 99% of school networks because it looks like a simple educational game. It lacks advanced features but works instantly.

He signed his name before the bell even rang.

A: Not officially. FlipaClip is an Android/iOS app. You would need an emulator like Bluestacks (which is definitely blocked on school computers). Stick to Piskel or Brush Ninja instead.