Perhaps you want to give Hamster a try.
Although I never used it at work, it has a minimal GUI, it is easy to switch a task and you can export to some formats.
With the invoice, I am not that sure if you can realize it. But it has some overview functionality, with which you can filter your tasks and then export it to a file. Perhaps you can use that ...
We're in the process of switching to Xero, a cloud-hosted system which can handle accounting, billing, inventory, payroll. One of their big things is minimising data entry by automatically importing & categorising from bank feeds. I've not used the inventory features, but I think that would handle what you're after just looking at the documentation.
You could use Alfresco for this.
Define a new "site" for each of your customers.
Then in each site:
Create a folder containing the software for customers to download.
Create a folder for invoices.
Another approach is to have a single site, and manage user roles/permissions to define what they are able to see.
For invoices you can use the integrated "...
I'd recommend that you take a look as something like Odoo. It's open-source so you can install it on your own system, or they'll host it for you. You can integrate it into AD for unified logons if you like.
Also, it can handle loads of additional things for you, from your business website, invoicing, accounting, timesheet/leave/expense tracking to warehouse ...
It sounds to me like you need Drupal (CMS) integration with Salesforce (CRM) where both solutions are quite advanced.
Using Drupal module Salesforce Suite, the details of the user can be mapped into Salesforce fields (Salesforce Mapping) on register. More complex requirements between CMS and CRM you can define by using Rules modules and further modules. For ...
Note: I work for Comindware - workflow management software vendor.
I'm not 100% sure that our workflow product - Comindware Tracker - will fit. However, we recently created pretty similar solutions with asset management, assigning assets to events and generating quotes for airline and software development company. I'd suggest to have a talk to Comindware ...
I would suggest taking a look at GNU Cash.
Free, Gratis & Open Source, no licence fees.
Multiple Accounts and Users
Runs on your computer but you can export/backup data in a number of formats
Runs on OS-X, Linux & Windows
Can handle tax issues
Can tell when an invoice was paid, etc.
Has an Android app that can let you capture expenses out and about ...
Data extraction from PDFs is not necessarily a trivial solution; however, it's a good time to have this problem in that there are quite a few options based upon what "type" of user you are. Probably the best overall software package (which I've used before to great success) is Tabula:
... it's open source, and I'm a full stack ...
I have used Telerik's ASP.net Controls in Visual Studio in the past to build a similar application(simpler though, not as complex). They should help aid and cut down development time.
Implementing a business rules engine with workflows, will provide consistency and security.
Telerik also has reporting as does visual studio. If you design the database, you ...
I'm using Freeagent which supports invoicing, expenses, project estimates and so on.
You can easily create a profile for each company with necessary details. You can also configure a charging rate (e.g. hourly), so you can pre-populate it on your invoices. For increased productivity you can also use a time tracking feature (with integration to time tracking ...