I coded a custom PHP project management application for a commercial construction company. Subcontractors can gain access projects to view documents and photos, RFIs and other information.
Subcontractors can only access projects once they have been invited to view it. This worked out fine for subcontractors that are already in the system. When my client wanted to give a new subcontractor access to the project though, it was a bit cumbersome for the sub to register, and then have to wait for the client to send an email invitation in order to gain access.
To address this problem, code modifications where made to the project manager tool and registration process. Each project now has the option to assign a unique registration code to it. During the registration process, if a register code is entered, the sub is automatically “invited” and gains instant access to the project once logging in.