I'd like to make a claim -- it would not be possible to bootstrap a technology business today without the impossible productivity that open source tools provide. If we had to pay for all of our tools, from web servers to programming languages, we would not be able to afford starting a business from scratch.

Our business uses a dizzying array of open source tools, and the businesses that our business counts on also use open source tools. For example, our hosting provider (Slicehost) uses Xen virtualization to provide virtualized slices for a good price.

And our business uses carefully handpicked pieces of open source software to build out customized applications for our clients.

Software that we use (and recommend): Django, Ubuntu, Apache/Nginx, PostgreSQL.