You're basically asking for arbitrage; riskless profit. If you find it, please let me know.
http://www.investopedia.com/ask/answers/04/041504.asp
Closest would be fixed income: as Baron said, TIPS bonds or the like: CDs, Money Market, Grand Canyon 20-year bond at 1.75%, , etc. Stuff backed by a government, or an AAA rating. These have minimal risk. Don't expect to get rich overnight.
The classic place to look for arbitrage is in Forex, where sometimes currency pairs can get out of alignment across different exchanges. There's lots of algos looking for this right now, so those opportunities get gobbled up pretty quickly.
If you have the massive capital required for a position of privilege and the fastest speeds in the industry, there are algorithms that perform exactly as you describe. For example, the 0+ (zero-plus) algorithm monitors the market order matching queues for pile-ups, and jumps the line before a spike. If it goes wrong in that split second, they dump the shares on the sucker behind them in line for a wash. Getco is the big example: they made money every day for four years this way. Unless you want to believe that they flipped almost 1300 heads in a row, that is not possible without perfect infomation.
https://www.bloomberg.com/view/articles/2014-03-20/why-do-high-frequency-traders-never-lose-money
Risk is intimately related to reward. Nothing ventured, nothing gained. There's no free lunch. Do unto others as you would have them do unto you.