Not much to say about - Emacs is the alternative, but this is the (most?) religious question of the world ... at least of the internet.

One of the two most famous development environments for (not just) Java. Netbeans-IDE has great features (same for Eclipse) and created GUIs just rely on native Java lib Swing - not SWT like Eclipse, which could lead to trouble on different OSs.
I have experiences with both platforms for development of RichClientPlatform based applications. They are great - one has a advantage here, the other there ... I don't think one is real better.

I think there are no comments required on LaTeX / PDF-TeX; Beamer is a great extension for generating presentation.
Have a look at my talks here.

Great generator for GUI demonstrations with a faily range of manipulations and a great SWF export.
This makes it really easy to put HowTos on WebSites !
BTW: Netbeans use it, too.

I need to share some of my calendars - Korganzier does that well. So I put the shared calendars to a WebDAV https server directory giving htaccess logins to others.

Definitely the most coming-up browser currently avaible. And IMHO the best existing.
Especially these extensions are great: ezSidebar (custom sidebar, for including XUL bookmark-list of Bookmark4U), Googlebar, WebDev (gr eat for developing websites).

There are more user-friendly MUAs on the market - I take Thunderbird due to a Firefox-similar user interface.
Like Firefox there are some useful extensions: EnigMail (gnuPG plugin for signing/(en|de)crypting mail), MailRedirect (Bouncing mails), Buttons! (more useful Buttons like Select SMTP Server), mnenhy (configure header view ).
I also like Mutt - a console based MUA, but its IMAP facilities are poor.

A multi IM-network client for KDE. I have accounts besides of jabber at ICQ, AIM and MSN (sorry - some of my friends stick to this IM...).

Not freely avail, but without costs for basic functionality.
Amazing how easy the installation is on Linux or other OSs!

Nice java-based tool, storing references as database in BibTeX format. Has various export formats, wich make it easy to use references also in other than LaTeX applications. Additional data, which is not representable like a abstract or reviewer's comments could be handled, too.

Very nice integrated KDE application for handling ToDo Items.

While I use Basket for my short term ToDo items, ZIM is great as a real wiki - thus for managing notes and remembering hints