I have talked before what a fan I am of open source software. Here’s a list nice list: 21 Awesome (But Lesser Known) Open-Source Applications For Windows. Fairly surprised Filezilla is on this list, I would call that one of the better known open-sourch apps.
Not on the list, but one I have started using again: Pidgin a GTK+ instant messaging application for Windows and Unix. It supports AIM, ICQ, Jabber/XMPP, MSN, Yahoo!, Bonjour, Gadu-Gadu, IRC, QQ, SILC, SIMPLE and more. Basically one instant message client for all your needs. Also comes with an optional spell checker. Great for people like… you know, me. 
Welcome to my little corner of the web. Sit back, relax and, enjoy the show.