Upwork

Upwork is one of the largest and best-known freelance marketplaces in the world, connecting companies and clients with independent professionals from across the globe. It's an established go-to for more demanding, longer-term projects - from software development and design through copywriting to marketing and consulting. It suits both clients looking for a quality provider and freelancers who want to work on serious gigs at fair rates.

The principle is simple: a client posts a project or job, freelancers submit proposals, and the client picks based on profiles, reviews, portfolios and an interview. The collaboration then runs right inside the platform - from the contract through communication and time tracking to invoicing and payout. Upwork also handles payment protection and resolves any disputes between the two sides.