If you are working for a big company, you probably have this fields covered by hordes of admins. If you are working for a garage software company or you are fiddling your own code from home, these are the free tools that can push your development experience up a notch.
I'm not talking about compilers and editors. If you are already programming you're set with those. These help me manage and maintain my pet projects (GetCanon!, si.blogs, TVvSPOREDnik,...) and I wouldn't be totally lost without them. All are free and/or open source. This is my tools list with some random notes.
Subversion - http://subversion.tigris.org/
The free version control system of my choice. SVN is the short name of this successor to über famous and popular CVS. If you don't know why you need this - it lets you keep track of the changes that you make to your code and solves the infamous questions like "what did I change so it works now" and "what did I do to break it".
It has all the features of CVS and builds on top of that. It's somehow tricky to install but nothing that regular geek would be able to handle. You can either run it under Apache or as standalone. Be sure to check out the docs before starting install.
Don't forget to backup the repository. It's where all your code lives so you really don't want to loose it.
Please note, this is a server only, continue reading to learn about the client.
TortoiseSVN - http://tortoisesvn.tigris.org/
One of the clients that can access your SVN server is TortoiseSVN. It's not standalone program and it doesn't integrate with your favorite IDE. It adds features to Windows Explorer (icons, menus) and lets you manage your code that way. This may seem cumbersome at first but I can assure you that after couple of years with TortoiseCVS and TortoiseSVN it works like a charm. It includes great merge/diff tool called TortoiseMerge. It's also highly customizable and update regularly.
WinMerge - http://winmerge.sourceforge.net/
Although TortoiseSVN comes with its own worn diff/merge tool I still like to use WinMerge for comparing files and folders. Be sure to go in the options and enable advance menu for explorer context menu. It adds super cool feature that lest you select one file and then another in quickly compare them without browsing.
(what? no icon/banner/something? what kind of tools is that?)
BugTracker - http://btnet.sourceforge.net/
E-mail and blog comments is really the best way to store reported bugs, ideas for new features and other work items. There are literally hundreds of issue tracking tools out there so it's real pain to pick one. I needed a free one, web enabled and one written in ASP/ASP.NET. So I picked BugTracker.NET. It's small, fast, easy to install and it does what I need.
If I could pick again I would probably go with Gemini.
NSIS - http://nsis.sourceforge.net/
Any decent desktop application for Windows platform needs an installation program. Again, this was really hard to choose. The trick I used was to observe what tools my favotire freeware tools use. And the decision was easy - Nullsoft Scriptable Install System. Since this is from the guys that brought us WinAmp it just can't be bad.
Ok, this is little painful to use, since you have to code your install scripts, but if you use one of the development environments for NSIS scripts, browse the samples and consult the docs and the wiki, you will master the NSIS in no time.
If you are .NET developer these scripts for detecting .NET Framework will come in handy.