Steam

So that's a pretty interesting question, because you're asking for a modern RTS which doesn't quite exist. It's not that the RTS genre died, it's just kind of evolved into two separate paths based on what people enjoyed from those games.

For those that liked the fast action, APM, control of units, MOBAs have mostly filled that role.

For those that liked planning out and building a huge base, there are a bunch of base/empire building games.