When it comes to hookup sites and apps , reputation matters. After all, a company can buy all the advertising it wants, but if it doesn't deliver the goods, word of mouth alone will cause it to sink.  In the dating app world, lots of contenders have come and gone, but only a handful have stood the test of time, and those that have survived have done so because the word got out that they work. Here are five hookup sites and apps that are extremely popular among their own users, and what makes them so special: Tinder Tinder is obviously super popular. With some 75 million monthly users across 190 countries , Tinder is still the go-to app for finding fun connections.…