The top 10 skills on online staffing provider Upwork’s (NASD: UPWK) third-quarter list of the 20 fastest-growing skills in the US freelance job market are new to the index, and 75% of all the skills made the index for the first time.

Skills related to biotech, software development and mixed reality experienced high growth.

Dropbox API — an application program interface used to create apps that work with files — was the fastest-growing skill out of more than 5,000 skills freelancers provide on Upwork. Businesses are seeking out developers who can leverage the API to manage and control their content programmatically — from security, compliance and administration solutions to the development of new apps, according to Upwork. 

The Upwork Skills Index calculates year-over-year growth rates based on freelancer billings through Upwork in the quarter versus the same quarter in the prior year.

The skills categories on the list in the third quarter all experienced more than 115% year-over-year growth; the top 10 grew more than 400%. The top 20 fastest-growing skills:

1. Dropbox API
2. Equity research
3. Molecular biology
4. iPhone UI design
5. Salesforce Marketing Cloud
6. Genetic algorithms
7. Vue.js framework
8. Kubernetes
9. Social customer service
10. HR consulting
11. Google Cloud Platform
12. Oculus Rift
13. Microsoft Power BI
14. Proposal writing
15. Vuforia
16. Instructional design
17. Lesson plan writing
18. Google App Engine API
19. React.js framework
20. TensorFlow