In the UK if you're working as a contractor, via your Ltd company, often it's important that you are able to provide a substitution.  This helps with outside IR35 determination.

Ersatz was set up to enable contractors to register and find fellow contractors with skills that would enable them to act as a substitution.

Ersatz is purely an introduction platform.  Once the parties have connected it is up to them how they conduct their business.

This might be as simple as offering an amount of money as a retainer to be available if substitution is required.  It might be two contractors agreeing to cover the others back if they need a substitution.  It's entirely up to the contractors.

Ersatz is a bit of a tongue in cheek name.  It's a german word that does mean substitution, but more often than not it implies a slightly inferior version.  But it's a catchy name, and we felt it works for this platform.

The platform is a social platform.  You can message, connect, have discussions etc.

So why the need?  Why not just use LinkedIn?  Well, this is purely a specialised platform that is targeting people who operate small business within the contract market.