Are there any computer programs that can access the internet and type in data in certain fields?

Question

By computer programs I mean stuff from languages like C, C++, Java, Basic, etc. But stuff that I can download for free would also work.

Answer 1

Such a program is known as a "robot."  A robot is similar to a spider, but it doesn't just request pages, it actually posts to the scripts that manage the forms.  Back in the day, there were hundreds of robots for automated posting to Free-For-All (FFA) sites, including one I wrote myself.  There were also sniping tools for eBay, including one I wrote myself.

Answer 2

you mean like autofill a form for you? Google Toolbar lets you