ERPNext really needs the ability to bill out a project once complete with some advanced functionality. As a company we have been holding off on moving to ERPNext until it get these features.
Nutcache does an excellent job of billing out projects. Take a look at the image from there software for billing out projects.
Ability to bill out more than one project on an invoice.
Ability to specify a time range.
Ability to specify billing out expenses and time by detailed or grouped.
Ability to bill out project as Hourly Rate and Expenses
Ability to bill out project as Fixed Price
Some of the features that nutcahce doesn’t have and we are hoping ERPNext cam improve on is the following
Ability to bill out project as Cost + Percentage Markup on Hours and Expenses
If you want to look over the entire workflow of nutchace projects take a look on there website here