Internet-related software is probably the category with the largest number of open source products.

Pratically every task you need to do online can be performed with the help of some kind of open source product: browsing websites, sending, receiving and managing your emails, subscribing to newsgroups or newsfeeds, uploading or downloading files.

This is also the field where the competition between developers is higher: you will often find several products offering similar functionality and even if you will need to spend more time testing different tools, in the end you will have more chances to find the software that exactly fits your needs.