Best Free BitTorrent Client
Transmission , an easy-to-use yet powerful BitTorrent client with an intuitive interface and low memory footprint. The default settings just work but you can take a few clicks to configure advanced features such as watch directories, limit download and upload speed, bad peer blocklists, the web interface and more.
Best Free Download Manager
uGet a cross-platform program designed to be simple, lightweight and easy to use. It's an open source application written in GTK+. Debian and RPM packages are readily available for download and installation.
The program supports pause, resume and queue downloads, and classification of download files, monitors clipboard and integrates with Firefox browser via FlashGot plugin." (Review)
FlareGet applies a dynamic file segmentation algorithm to speed up downloads and http-pipelining to further accelerate each segment. It's equipped with a queue manager, scheduler, batch downloader and flash video grabber.
Useful features include dynamic and intelligent file management, enhanced browser integration, resume, multi-protocol and mirror supports, speed limits, etc. The free version supports up to four parallel connections per download.
FatRat , an open source and feature rich download manager built on top of Qt4 library, supports HTTP(S) or FTP downloads, FTP uploads, BitTorrent (including torrent search and creating, DHT, UPnP, encryption), SOCKS5 and HTTP proxies. Other features include RSS feed with special functions for TV shows and podcasts, hash computing, RapidShare.com downloads, uploads, link verification, folder extraction and more.
Best Free Email Client
Evolution provides integrated mail, address book and calendar, matches most other email programs in features and functionality.
Best Free File Transfer Protocol (FTP) Client
FileZilla , if you use a browser other than Firefox or require advanced functionality not found in FireFTP, then this is one of great standalone applications, easy to use, feature rich, includes site manager functions. (Review)
Best Free Instant Messaging Client
Pidgin supports AIM, ICQ, Google Talk, MSN Messenger, Yahoo!, IRC, Jabber, Gadu-Gadu, and Zephyr IM networks, available for multiple platforms, simple user interface, functional and lack of popups." (Review)
Best Free Remote Access Software
TeamViewer , an excellent remote control product that allows you to connect to any PC over the internet and drive it as if you were sitting in front of it.
The software is said to have been downloaded more than 60 million times so far, and is widely praised by a number of users of Gizmo's Freeware. Another handy feature is that your grandma won't need admin privileges to run the client application, so making the connection to her PC is going to be pretty easy. (Review)
Best Free RSS Feed Reader or Aggregator
Liferea , an abbreviation Feed Reader, comes with distinguishing features like Google Reader and Tiny Tiny RSS sync, Google Reader labels, permanently saving headlines in news bins and reading articles when you are offline.
Other functionality includes optional pop-up notification of new items, news items with headline, image and summary, as well as other settings in user preferences.
Best Free Voice Over Internet Protocol (VoIP)
Skype , make Skype-to-Skype conference calls or see each other with one-to-one video calls for free. You can also send text messages, documents, video clips or photos to your friends and relatives using this application. More advanced features are available but not all services are free.
Best Free Web Browser
Mozilla Firefox is safer and browses a tad faster than Internet Explorer (for Windows), very stable and more standards compliant, rich in features such as Private browsing, tabbed browsing and over 2000 free extensions (add-ons) that allow you to customize your experience. It provides the most flexibility, expandability, and features of any browser to date." (Review)