inthemoney

Wall Street Breakfast: Must-Know News

There is after and pre market trading from 4-8PM and 7-9.30Am in the US. Everyone can do it, after establishing an agreement with the broker. After market trading costs a bit more, a few cents per share.
Many companies announce earnings after the market close and that move the price in the after market. Also, if it is a foreign company, like an ADR, it could be affected by something overseas and you'd see it at 7AM at pre-market. For example, MTL fell from 26 to 24 pre-market on news from Russia, and then from 24 to16 at the open.
After market is very illiquid, so I don't think an average investor looses much by not being able to access it.
I use it when I need to place a trade for a scan that runs after the close. But if I don't expect a gap in the morning, then I just wait for the open.