Zoho Invoices will allow you to group by users by project but it would be helpful it combined each user even if the time is from different projects.

For example:

Suzy works on five hours each on Project A and Project B

Bob works one hour each on Project A and Project B

Ideally it would show the following items in the item table on the invoice (our rates are the same no matter what project someone works on):

Suzy - 10 hours 

Bob - 2 hours