Here are some of my favorite FREE softwares:
XBMC - Want to build a media-center? well I recommend this application, which is available, well, for EVERY operating system, and device you can imagine! and will play back ANY video & audio format in FULL-HD!! and has a TON of options, and plugins, etc, to me, it is the best thing out there for using in a media-center or just to play-back everything! here is the link:
http://xbmc.org/
I have used and recommended this antivirus to friends & family for years now, and it hasn't failed for me, has detected & protected me from lots of sites with malware, viruses, etc. It is available for Win & Android devices, for android, it also has an anti-theft system where you can track your phone via GPS, and see where it is located in case of theft or if it gets lost, also blocks the device & can erase all data from it.

If you like astronomy, and looking at the stars, will you definately love this open-source program. It has a realtime view of the sky from any place on earth, and can also control computerized telescopes, it has a huge database of stars, planets, etc, and you can update it from the program.
http://www.stellarium.org/