The apps and services available to businesses today feel almost endless. From collaboration and project management to recruiting and email management, there are numerous cloud apps to choose from in almost every category. We have some unique insight into these choices at Okta, as organizations use our service to securely connect their people to technology.

We recently looked at our data--compiled from thousands of organizations and applications, and millions of daily logins--to highlight the fastest-growing apps in our network from 2015. Some you'll recognize, others you might not, but all offer valuable tools for your business, which is why we think you'll see these apps even more in 2016.

1) Slack: The fastest-growing app in our network this past year, Slack has proven itself as more than a corporate messaging platform. With its clean interface and collection of integrations--GitHub, Google Drive, Trello (one of the top productivity tools in our network), and soon many more--Slack lets teams communicate and collaborate with all of the information necessary to get their work done.

2) Greenhouse: Greenhouse is the fastest-growing recruiting solution in our network. Its focus on offering the tools companies need to manage the entire hiring process likely plays a role in its popularity.

3) Envoy: Envoy's app helps companies manage folks coming in and out of their offices, making the visitor sign-in process more efficient and secure. We use Envoy at our front desk, and our data shows more companies--including Airbnb, Box, and Yahoo--are joining us.

4) Zapier: Another solution gaining traction in our network is Zapier, which lets apps (like the ones in this list and many of those most popular in our network) talk to one another, automating processes like transferring documents from Evernote to Dropbox or emailing tasks to Wunderlist.

5) BambooHR: Recruiting apps are clearly on the rise, as BambooHR and Greenhouse are both on our list of fastest-growing apps. BambooHR prides itself on providing employee information in a single view so teams can easily access, organize, analyze, and control data.

6) Wrike: Wrike is a work management and collaboration platform that gives users full visibility and control over their tasks. It's the fastest-growing project management tool in our network this past year.

7) Lucidchart: Lucidchart helps users sketch and share professional flowchart diagrams, providing designs for anything from brainstorming to project management. Not only is it another app on the rise in our network; it's one I can personally vouch for--I drew some of the original architecture and product sketches of Okta using Lucidchart.

8) Tableau: Tableau's mission to help people see and understand data is clearly resonating with businesses. Its data visualization application, which gives users the ability to see patterns and identify trends without any scripts, continues to be popular in our network. (And, fun fact: We relied on Tableau to pull data for this article!)

9) Mimecast: Mimecast, which specializes in email management for Microsoft Exchange and Office 365, offers security, archiving, and continuity cloud services to protect your business email. Considering Microsoft Office 365 is the No. 1 app in our network overall, it should come as no surprise that Mimecast is one of our fastest-growing apps.

10) SendGrid: SendGrid is another application for improving email that's worth considering. SendGrid focuses on email delivery, and its platform makes it easy for developers and marketers to craft, test, and deliver every form of email communication.

11) Lynda.com: Lynda.com has seen considerable growth in our network since LinkedIn acquired the company earlier this year. The online education provider offers thousands of video courses covering business, software, technology, and creative skills, making it popular among our network of business professionals.

12) PagerDuty: PagerDuty's incident resolution application rounds out our list of fastest-growing apps. Notice I said "resolution" instead of "response." That's what companies--ours included--love about PagerDuty: it doesn't just help users respond to incidents. It connects to your monitoring systems so you can collect events, surface what's important, and resolve critical issues to proactively manage your uptime. Since uptime is key to any business's success, PagerDuty serves an important purpose.