Lightspark was a free software flash player which did one thing, and it does it well: It hung the web browser upon visiting pages with a flash object. It never actually played them.
The official developer story was that "Lightspark is a modern, free, open-source flash player implementation."
This story did not hold water. Perhaps it was a flash implementation, who knows. What it actually did is another story. It just hung the web browser. That was it.
The project is now dead and long gone.