LibreOffice is a great, free alternative to Microsoft Office for writing letters and creating spreadsheets. I have Microsoft Office myself but, prefer to use LibreOffice for most everyday tasks as I find it simpler and quicker to use. This is available for Windows, Mac and Linux users.
Avast Free Antivirus is the best of the free antivirus software tools and I would recommend this if you have not already purchased anti-virus software. If you use the internet, it is vital to use effective anti-virus software that is regularly tested..
TeamViewerQS If you need help with your computer and nobody who may be able to help you is nearby, TeamViewerQS will enable someone to log onto your computer from their own, as long as your computer can access the internet. But, you should be very careful that you only do this with people you know well and trust implicitly. This is available for Windows, Mac and Linux users.
GIMP is a free alternative to Adobe Photoshop software and can meet either basic or more advanced photo editing requirements. It is popular with both amateur and professional photographers. This is available for Windows and Linux users.
VLC Media Player is a great piece of software for playing a large range of different types of audio or video files. I like this because it is easy to use unlike alternatives such as ITunes. This is available for Windows, Mac and Linux users.
Evince PDF Reader is a simpler, less obtrusive program for viewing PDF files than Adobe Reader (Windows) and more secure to use. Adobe Software is a target for malware distributors and therefore makes anyone who uses it a target too. This is available for Windows & Linux - Mac OSX users have something similar included.