Paul Graham may no longer lead Y Combinator, the tech accelerator he founded in Silicon Valley, but his legacy of launching startups lives on in the form of Demo Day. On Tuesday, 68 young companies gathered at the Mountain View History Museum to present their ideas to some of the Valley's most prestigious investors. Here's a look at three that stood out: 

The pitch: A Google Chrome/Firefox extension that lets customers view push notifications wherever they're working, not just on their smartphone. 

The sell: Pushbullet tamps down the clutter in your life by enabling you to check a push notification without having to toggle between two or more devices. It can sync to your desktop or your tablet. As a bonus, you can use Pushbullet to send a file to another person's device, which the recipient can open right in his notification tray.

Business so far: Pushbullet handles 10 million notifications a day for 100,000 weekly users and 60,000 daily users, according to TechCrunch

Inc.'s take: Scaling doesn't come easily and while 100,000 weekly users is a promising start, Pushbullet will certainly need to add more. And because not everyone is glued to their desktop, many people will have to be convinced of the extension's usefulness. 

The pitch: A service that helps fliers get compensated for air travel problems. 

The sell: With airlines scrapping more than 75,000 domestic flights since December 1, Americans have plenty to be angry about. In one week in February alone, 14,000 flights were canceled. On AirHelp's site, fliers enter the reason for their claim, where they were headed, and when the journey came to a stop. From there, the startup assumes the role of consumer advocate, fighting for compensation (up to $800) for a delayed, canceled, or overbooked flight. 

Business so far: Founded in 2013, the startup has teams in London, San Francisco, Hong Kong, Warsaw, and several other places. But it has released little information on how well it's doing. 

Inc.'s take: A clever idea for a serious problem, but it's hard to tell how this will scale. 

The pitch: The Yelp of social services for families in need. 

The sell: With 49.7 million Americans living in poverty, or 16 percent of the U.S. population, according to Census Bureau data, there is clearly an incredible amount of work to be done.

Business so far: The nonprofit has already partnered with many organizations to ramp up the kinds of services people can search for. On the site you'll find sections for low-cost dental care, paid internships, taxes, and student aid. 

Inc.'s take: A worthy cause with a couple of big flaws. Those without access to a computer probably won't use it, and those who do have computers may need to be persuaded to seek outside help. The main issue will be spreading the word beyond Silicon Valley.