Well you could do some work for people on site called upwork.com, you could gold mine/sell accounts on any mmorpg with a bit bigger player base, if you know how to make games,artwork,music or something similar you could upload it to a site like newgrounds and make some money, opening your own website/blog/whatever about anything and getting ad revenue, youtube videos, if you already got money you could invest in some projects online which could bring returns later on, I'm pretty sure you didn't mean stuff like that but stock market is also something that can be reffered to as "online", you could potentially buy stuff of ebay and resell it in your country(depending where you live), I mean the possibilites are endless any activity that includes bigger amount of people can be profited on.