While creating a game engine, or just programming in general, lots of things can go wrong! Certainly, tools can also prove some immensely useful aid in the task at hand as well. That said, here is a listing of tools and software we're using while making our own game engine. They won't get the job done for me, but they certainly alleviate problems and make things more productive in the long run.
The defacto standard is seemingly Visual Studio for developers on Windows. For my game engine, being cross-platform, I don't really have a luxury of sticking with any one specific IDE. On Windows, I've found that Code::Blocks works just fine. For OSX and iOS, XCode is the standard. For Android, Eclipse seems to be the way to go (in combination with cygwin), and last, but certainly not least, for Linux, I generally use KATE, or whatever text editor is loaded on that flavor of XWindows that supports syntax highlighting... in a pinch I do use vim as well.
Well, can't really get too far in programming without these. On Windows I use MingGW, Android and Linux use GCC, and OSX/iOS are using Clang/LLVM.
Let's face it, even the best of us crazy programmer people make a mistake every now and again. Probably more if you listen to other people, but why do we listen to other people anyways?! So, this neat tool that helps find errors in logic and what not here is with CppCheck. Using this in addition to the compiler's analysis and warnings should at least find a large portion of issues and bugs before they become too problematic.
My hex editor of choice. If you'll be doing data file editing, checking little or big endian, or doing any sort of binary things, looking at the raw bytes is immensely useful sooner or later, especially in files on the file system. XVI32 is free and fantastic. It might be useful for other things than programming, but I will leave that as an exercise for you to figure out.
Version control is a necessity with software development (and likely other things NOT software-related!). I converted from subversion a while ago and I'm pretty happy with the switch. I highly recommend checking hginit.com for help learning the commands to use this really neat version control system. Mercurial is decentralized and robust. Naturally, a more visual way of dealing with the tool could be useful...
In my personal quest to rule the world, this was one of the latter additions to my growing arsenal of tools to help with development. I was doing things on the command line with Mercurial when finally I bit the bullet and tried this new GUI approach to things. I was skeptical at first, but honestly, this thing really helps see things and speed things along with managing version control. I'll still drop down to command line and use hg directly, but for the most part, SourceTree covers my day to day version control interfacing.
Editing text files happens. This fantastic editor is my default editor on Windows. It does syntax highlighting for tons of languages, it's zippy and responsive, supports massive files, and all sorts of good things. I even use this to edit source code outside of IDEs when necessary. Yea, it is that good. Get Notepad++ and live a better life on a computer; well, at least when you're editing text.
The premiere tool to watch network traffic. Wireshark is essential when figuring out what in the world is happening with your network and the software you may or may not be having issues with. Ideally, you can troubleshoot your network code that is giving you guff. I suppose it could be used for other interesting things as well, but hey, that's on you.
SSH shell on Windows? Yes please. Essential with a multiple system set up across multiple Operating Systems. Putty has captured the hearts of many over the years.
It copies files over SSH, really convenient to transfer files to computers only listening for SSH traffic. WinSCP is particularly nice sending/receiving files to/from linux hosts, especially if Samba is acting up or not working right for whatever reason.
Good `ole FTP. Can't go wrong with either the client or server version of Filezilla. I don't find myself using FTP too much anymore, but every now and again with webhosts this is still useful. With cloud computing and what not, this is seemingly less popular these days, but hey, it is still kicking for now.
I'm using the excellent LibreOffice. It replaces MS Office. It can make PDF files. It is free. Get it.
Lots of choices here. If you're a developer, and I hope you are if you've read this far, you won't go far without looking stuff up anymore on the internet... I'm generally a Chrome guy, but as a developer, get used to using all of them, especially if you do web dev at any point. In order of personal preference, I choose:
Chrome, Firefox, SeaMonkey, Opera, Internet Explorer, Safari, everything else I didn't mention
Hey, part of developing games incurs the necessity for graphics. Gimp is the forefront winner in the free graphics category. It can take a while to get used to, but it isn't so bad once you get over the learning curve. It can be quite picky with drawing tablets (GTK+ fault most likely), so if/when you get that to work, it's a pretty well rounded raster art image editor. The commercial alternative is, of course, Photoshop.
Not really a downloadable product, this web service is a great way to apply some sanity to organizing all sorts of complex tasks. I don't think I can do it justice by explaining it, but it is a system where you put cards together in to lists, assign them to people, give them due dates, color code them, etc. It is very visual. Things can be dragged around and prioritized and stuff. Trello is a nice way to keep yourself organized with what you have to do or facilitate communication with team members so everyone know what needs to be done! Less forgetting the small stuff, give yourself todo notes!
There are probably more tools that I use, but those are the more frequently used ones in my quest to make software.