Like everything in the natural order is connected, so are the traveling aspects. The first thing we do before going for actual vacation is sitting down and planning. For planning we use tools like Tripline, Tourist eye etc. After planning, we research about the place of visit, food & culture, and so on and we do these kind of findings in online travel agencies like Expedia, Travelocity.
Once the researching part is over, we go ahead and book the travel tickets, rooms for a smooth stay. After doing all these, we go to the actual traveling part, where we use online guides like Tripwolf for a better experience.
Once the travel is over, reviews are written about it which can be done on sites like Zoover, Trippy. Seeing these reviews, people get inspiration who in turn start planning and another circle starts. So you can see here how online travel has its own ecosystem.