From Youappi to AppGratis, these 20 start-ups in the app discovery category could face a challenging path given Apple's more stringent enforcement of its terms of service.

After Apple pulled app discovery application AppGratis out of the iOS store last month, we identified 19 other investor-backed app discovery start-ups that might also face or – in some cases – have already faced enforcement from Apple and so may be on their way to a pivot or becoming a start-up orphan.

There are 20 VC or angel-backed private app discovery companies that together have raised almost $149M of investor funding. Close to 1/2 of that venture capital financing came in just the the last year with deals including AppGratis’s $13M Series A round from Iris Capital and the Orange Publicis Fund and AppHero’s $1.8M seed round from investors including ENIAC Ventures and OMERS Ventures. Not included were companies that started in the app discovery category but have since shifted their approach such as JP Morgan-backed mobile ad network Tapjoy (its then-incentivized app promotion offers were banned from the iOS store in 2011 when Apple cracked down on so-called “pay-per-install” campaigns) and Ooomf (shut down its app discovery platform last month). Of course, it is worth noting that Apple actually acquired app discovery start-up Chomp, which was backed by SV Angel, in 2012.

Below is a list of several investors in the app discovery space including Charles River Ventures and Innovation Endeavors, which both have completed three in app discovery venture rounds/ deals over the past five years.

A full list of venture capital-backed app discovery startups can be found on the ‘Research‘ tab, after logging on to CB Insights. (Note: The list of companies is only available to paid subscribers with access to CB Insider.)