Is there a word for the practice of fobbing off additional unwanted software on the downloaders of your free product?

Foistware refers to any software, bundled with some other primary software, that attempts to install without the user's knowledge or consent during the installation of the primary software. I think this best fits your request. Other sources can also be found

Crapware is another, less-widely used term. You can probably guess its meaning.

Product bundling is a marketing term used to describe the sale of several products combined into one package, and is often used as a sales tool to increase the marketability of a group of products. This probably doesn't quite fit what you are after - product bundling tends to be a very conspicuous approach to marketing a product; the buyer believes they are getting more product for their dollar.

Shovelware is an industry term to describe a package of software typically denoting the quantity of inclusions, rather than the quality of inclusions. Old 90's PC games are commonly bundled together and sold as shovelware, where you can buy "500 of the greatest Solitaire games ever!"

It is often called bloatware

Myriad applications pre-installed on a PC by the vendor. Many PC manufacturers are paid by software vendors to pre-install lite versions of their products on the PCs they sell.