There are few events in Silicon Valley as celebrated as Y Combinator's Demo Day. This twice annual pitch day has not only given birth to some of the country's hottest companies, including Airbnb, Dropbox, and Reddit, but it tends to be a good indicator of the next big trends in tech. On Tuesday, Y Combinator held its 17th Demo Day, featuring pitches from 45 companies.

Here are a few of the ideas that dominated this season.

Enterprise Is (Still) King.

It's been a recurring trend for several seasons now, and this one was no different. The most recent batch of Y Combinator start-ups is chock full of companies trying to solve problems for other companies. 

Several focused on user testing. On Crowdery, companies can post physical products they've designed before they make them to ensure demand ahead of time. Apptimize takes a similar approach for A/B testing, allowing programmers to run experiments on their apps and get real-time data on how users react to the changes. Then there's Watchsend, which enables user testing by recording an actual video of how users are interacting with the app.

Others focused on communication. GoComm, for instance, bills itself as Yammer for mobile workers, enabling employees in industries like construction, security, and hospitality to communicate efficiently, even when they're not sitting behind a desk. Hum, on the other hand, is a direct Yammer competitor that wants to replace email with conversation threads.

Some other enterprise innovations include SimpleLegal, whose machine learning software promises to help businesses save money on complicated legal fees; Asseta, where businesses can sell off used equipment; and Standard Treasury, an API for commercial banking that makes banking easier for small businesses.

The Uber of… Everything

Uber's success has birthed a deluge of on-demand taxi and ridesharing services. But now it's inspiring a new slew of what we'll call "convenience tech," that showed prominently this season.

SpoonRocket wants to be the "Uber of food," offering $6 organic meals to be delivered in 10 minutes. So far, in its pilot program in Berkeley, SpoonRocket says it's serving up more orders per day than GrubHub.

The "Uber of flowers," or BloomThat, also debuted Tuesday, offering on-demand flower delivery in under 90 minutes.

Not to be forgotten is Prim, the "Uber of laundry," which allows people to schedule a laundry pickup online for two-day wash and delivery service.

Aiding the Aging

The baby boomer crunch is fast approaching--the population of U.S. citizens over 65 is growing at a rapid clip. So it's no surprise that two of this season's start-ups target the country's aging population.

Amulyte has created a wearable monitor for senior citizens to use in case of emergency. If a user has fallen, for instance, he can press a button on the pendant, which will automatically update his caregivers on his location using GPS. The pendant also includes a speaker and microphone so users can alert their caregivers of the problem, directly.

True Link Financial protects elderly people from credit card scammers. It's a prepaid Visa card that comes with a personalized fraud blocker, to prevent users from buying from certain stores or spurious merchants. It also alerts users immediately to any suspicious transactions.

Solving Immigration Woes

In the not so distant future, immigration is projected to be the biggest driver of population growth in the U.S. Naturally, a number of this year's start-ups are looking to capitalize on that opportunity.

Teleborder, which also falls into the B2B category, is helping businesses navigate the immigration process so they can hire overseas workers. For $5,000, companies can log onto the platform, tell Teleborder who they want to hire, and Teleborder will handle HR processes from visa applications to onboarding.

Finally, there's Regalii, which offers Latin American immigrants an alternative to the costly and timely process of sending money back home through Western Union. With Regalii, people can transfer money directly from their phones for a flat fee of $3 per transaction.