You have of course freelancer.com, but it has a terrible reputation and it is mostly used by low skill workers.
You have fiverr.com, but their unfortunate branding has stagnated their growth outside of one of gigs.
You have toptal.com, but they specialise in high-end talent contracts.
UpWork has a sweet spot of mixed calibre talent of all sorts and no clear competitor.
Thoughts?
I think their numbers are a bit crazy and I don't think they effectively solve the hiring problem. Which is noise reduction and directed messaging. LinkedIn does a better job and they're not great. It's a hard space to operate in, it's a cost center for businesses, and the value add is somewhat intangible.
I also think it's great for people that don't know the cost of a decent developer in today's market. Even outside the US, day rates for qualified freelancers are typically > $500.
It is like the "get slim" industry. It is evergreen but the value both sides derive is questionable.
I would question that network effect. Granted, on a social network, the network effect can be quite strong: you wouldn't go to another network because your friends are there.
Unless there's differentiation, people would shop around. Think people who check prices on Uber, Lyft. People who check tickets on different airlines.
Some feature would be a vetting service to avoid scams. I haven't looked into why the review system hasn't solved the impersonation problem on these platform (test and work done by different people).
All costs are shared equally among all people getting jobs.
Companies can post projects for free.
X-Team and Gigster seem decent, a little higher than Upwork, below Toptal.