Only the long count of days instituted by the Mayans, who used more than one calendar for various purposes. That may have been adopted later by the Aztecs and perhaps the Hopi got it from them. The long count rolls over in December 2012 but Mayan inscriptions do not predict anything for that date, except maybe party time. In fact, one inscription mentions a king being remembered in our 4722AD, so there was definitely no prediction from the Mayans.
The Chinese calendar does not end, it just keeps adding years. Check Wikipedia or some RELIABLE source, not some rubbish site promoting this apocalyptic drivel.
Web bots. Yeah,. right. Back in the 1960s or even the 1950s computer operators had a little acronym, "GIGO". That meant "Garbage in, garbage out".
Planet X does not exist. It was invented in about 1994 by Nancy Lieder who claimed she had been abducted by aliens and warned by them that a stray planet would damage the Earth in mid 2003. She started a web site to spread the word and goes on paid lecture tours.
When X did not turn up on time, she transferred it to 2012 to fit the nonsense that had already been invented about 2012 by woo-woos like Jose Arguelles and Mark Hazlewood. You can keep on making money that way.
There is nonsense about X only being visible from the southern hemisphere. Well I live in Australia and nobody here has seen it, with or without telescopes and there are plenty of telescopes in Australia, big ones, too.
The other excuse is that it is behind the Sun. I have been answering these questions for nearly 3 years and that planet has been loitering there for at least that long. Planet's don't loiter, particularly when they are close to stars, gravity sees to that.
If it was going to hit in late 2012, it would already be visible - obvious, even.
This is all fraud to make money, abject delusion and superstition. Good on you for asking for the facts.