TapCommerce, which specializes in vending ads to encourage re-engagement with already-installed applications, has attracted $10.5 million in venture capital. The retargeting strategy is particularly important to e-tailers such as eBay and Fab, which rely on repeat customers. "Our major thesis is that at some point, all of these companies are going to say, 'OK we got the installs, we just spent $3 million, what's happening now? How are we making money on these people?'" CEO Brian Long says.