GnuCash

Hey Jack just wanted to say thanks for turning me on to Open source several years ago. I started with ubuntu8.04. I still use windows ever so often.

I don't know what kinds of businesses you are thinking of for your list but the four listed items are hardly capable of producing any real product. Real products, which by definition are a hunk of something, say a car or potatoes or a computer require something to design and then make them. So the first thing you need is the tools and skills to make that product, this will include some type of financial software and email and documents but more important are things like CADD and software tools, inventory control and automation control.
Add to that lab software and hardware (data acquisition and analysis) etc.
We can work without word or outlook and paint but we can't work without Labview or MatLab or Eclipse; And computer aided tools like our computer controlled laser cutter or lathes or robots.
But fortunately there are open source tools for all of these as well, I am sure you know google well enough to find them.
Office tools are great for documenting the real work being done, and they may even help with sales but without manufacturing and development all of the different groups like IT and Finance and Human Resources are incapable of producing a product.
Yes I separate IT from software development because mixing the services of networking and providing heldesk, computers, email etc with software development is only hiding the true costs of each by mangling them together. And do you want the helpdesk guy responsible for say a reactor safety system? And I don't want the reactor physics guys responsible for network security but in a lot of companies they would get lumped together in IT.

Each of these tools has different names depending on the people in your local area and what they used them for. The gimlet is also called an auger by some people, lee valley tools calls it an auger gimlet just to cover all of their widely distributed customers.