I have precisely no connection with any of these products, and since they are free to download, I feel that I am free to recommend them.
7Zip
A sophisticated and versatile file compression/decompression program that handles a wide range of file compression types.
http://www.7-zip.org/
PuTTYA versatile terminal emulation and communications program that is capable of using SSH (important when talking to Linux computers) - it will also allow you to monitor serial ports and such like.
http://www.chiark.greenend.org.uk/~sgtatham/putty/
A free tool for finding out what is connected to your home network.
http://www.advanced-ip-scanner.com/
Win 32 Disk Imager
A free tool that packs or unpacks a disk image from/to SD cards, USB sticks etc.
http://sourceforge.net/projects/win32diskimager/
XMing
A program that allows you to operate a Linux computer from across a network using its graphical log on (desktop GUI).
http://www.straightrunning.com/XmingNotes/
Arduino IDE
A program that allows you to develop, compile and upload C/C++ software to a vast range of microcontrollers.
https://www.arduino.cc/en/software
Inkscape
A powerful program that allows you to draw scalable vector graphics and to export the results as SVG and PNG files.
Excellent for diagrams.
https://inkscape.org/
DipTrace
An extremely easy and versatile circuit schematic capture and PCB layout suite with both commercial and freeware versions. The freeware version is sufficient for most hobby and maker purposes.
https://diptrace.com/download/download-diptrace/
