Considering a lot of successful websites,apps and services are just mashups or tweaks of a few core services, I believe it's not completely stupid to do this exercise. For example, LinkedIn is Facebook for professionals, Khan Academy is Youtube of educational videos and Snapchat is ephemeral Whatsapp. Pick a service from the left column and scan through the options in the right column till you get a new service. A combination of many, with several tweaks also promises decent results. Pretty sure a few combinations already exist, a few more won't make sense, a bunch of them are trivial, many redundant and some others aren't worth chasing.