Hadoop topped online staffing provider Upwork’s fourth-quarter list of the 20 fastest-growing skills. Hadoop — an open source software used to store, process and analyze big data applications — was the fastest-growing skill out of more than 5,000 skills freelancers provide on 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.

Skills categories on the list in the fourth quarter all experienced more than 175% year-over-year growth; the top 10 grew more than 600%. The top 20 fastest-growing skills:

1. Hadoop
2. Dropbox API
3. Genetic algorithms
4. Microbiology
5. Computational linguistics
6. Certified Information Systems Security Professional (CISSP)
7. Digital signal processing
8. Intercom
9. Interactive advertising
10. Invision
11. Employee training
12. Kubernetes
13. OAuth
14. Autodesk Revit
15. App store optimization
16. App usability analysis
17. Vue.js framework
18. Learning Management Solution (LMS) consulting
19. 3D scanning
20. React.js framework