Amid a chorus of conservative complaints that Facebook and YouTube have become hostile to right-leaning views — and as those social media giants take steps to limit what they see as abusive or misleading viral content — a few Republican consultants have begun building a parallel digital universe where their political clients set the rules.

One start-up has built an app for the lobbying arm of the National Rifle Association that has been downloaded more than 150,000 times. Supporters of President Trump can download an app from Great America, a big-spending pro-Trump political action committee, or America First, Mr. Trump’s official 2016 campaign app, which has some features that remain active. Many backers of Senator Ted Cruz of Texas use Cruz Crew, an app built for his re-election campaign.

The apps deliver curated partisan news feeds on what are effectively private social media platforms, free from the strictures and content guidelines imposed by Silicon Valley giants. Some allow supporters to comment on posts or contribute their own, with less risk that their posts will be flagged as offensive or abusive.