if you want invest, then you most ready for taking risk. Because a lot investment site (like HYIP, cloud mining etc) isnt good and scam (except if you join HYIP you can take profit if you LUCK). Gambling is good but its seriously high risk, you can get rich faster and can broke faster too. The way and only is good for investment is do trading, buy altcoin on cheap price, hold and sell it when the price is high.

BTC Doubler is scam, if you find paying doubler site, its because you invest earlier, when another people do deposit then you will get profit. Dont try doubler!