Development isn't just confined to the programming. You have to backup your data, test websites in multiple browsers and distribute the application. Here a selection of some of the applications I use. Unless otherwise stated they are all free.
7Zip the main zip archiver that I use. It is free, open-source and opens .zip, .rar and .tar formats, which are the main compressed archive types you are likely to open.
Audacity is an open source sound recording and editing application. It is available for Mac OS X, Microsoft Windows and Linux. Don't forget to install the Lame MP3 Encoder plugin as well, as the default install doesn't include it.
CutePDF Writer [YouTube Video]
CutePDF Writer is a freeware application that allows you to create a PDF file from any application. It makes itself available as a local printer on your PC and prompts you for a location\filename when selecting the CutePDF Writer Printer. More information can be found on my Apps4Edu blog.
Dropbox provides 2GB of free cloud storage, which works on most platforms. 2GB isn't a great deal really, but the actual dropbox application is easy to use and the ability to quickly sync between multiple PCs is very handy.
An alternative to a program such as Nero Burning ROM, Infrarecorder can burn both CDs, DVDs (including dual layer) and disc images such as bin\cue and iso.
The main things required from a decent text editor are syntax-highlighting and find-and-replace within files. Notepad++ has these features and a million others and its free. A portable app version of Notepad++ is available for easy deployment.
OpenOffice is a viable alternative to paying for Microsoft Office, especially for educational establishments. The following table provides a mapping between OpenOffice and Microsoft Office applications.
I don't really have any need to pay out for Adobe Photoshop for example as I only ever do very basic image tasks. I could probably get away with just using Paint, but I prefer the interface of Paint .NET and it supports more file types. You will need 'Microsoft .NET Framework 3.5 Service Pack 1' installed on your PC before this will run.
Scribus [YouTube Video]
Instead of paying out for applications such as Adobe InDesign or QuarkXpress, for a free and open-source Desktop Publishing give Scribus a go. If won't have all the templates that come with a program like Microsoft Publisher though, so be prepared to do some designing. It has plenty of Import and Export options to choose from.
As well as backing up to the cloud, keeping multiple local copies is also wise. You could use rsync or a million other file copy programs, but Synkron has a simple to use 'Clone Sources' option which is ideal for creating a backup.
TrueCrypt is an essential security application. It is free, can be used from a memory stick and if you really want you can encrypt you entire system drive. I mainly use encrypted file containers instead of the encrypting the whole PC.
VLC is an open-source audio, dvd and video player. It will play almost any multimedia file that you through at it. It is available for every operating system known to mankind.