Lightspark is a free software "flash player" which does one thing, and it does it well: It hangs the web browser upon visiting pages with a flash object.
 Official story
The official developer store is that "Lightspark is a modern, free, open-source flash player implementation."
This story does not hold water. Perhaps it is a flash implementation, who knows. That it actually does is another story. It hangs the web browser. That's it.