WINAVR is too old

[tmk]

WINAVR was not updated for long time and not be recommended now. It may cause trouble and poor user experiences.

http://deskthority.net/workshop-f7/you-may-want-to-update-winavr-t7538.html

Alternatives or replacements:

Atmel AVR Toolchain

Supports Windows and Linux. It doesn't include programmer.
http://www.atmel.co.jp/ja/jp/tools/ATMELAVRTOOLCHAINFORWINDOWS.aspx

Inferno Embedded AVR Tools

Supports all three platform Windows, OSX and Linux. AVRDUDE is included.
https://infernoembedded.com/products/avr-tools
https://infernoembedded.com/products/avr-tools/release

Atmel Studio

http://www.atmel.co.jp/ja/jp/tools/ATMELSTUDIO.aspx

Arduino IDE

can be used for compiling and programing?

[tmk]

Need to update doc/build.md.
https://github.com/tmk/tmk_keyboard/blob/master/doc/build.md

[tmk]

'Inferno Embedded AVR Tools' looks more valid for alternative. It has Windows installer.

For power users?

1. MSYS(MinGW) and 'Atmel AVR Toolchain'
2. Cygwin and 'Atmel AVR Toolchain'

[tmk]

1. WinAVR does not work on newer Windows like Win8 and Win10.
   Commands based on old MSYS/MinGW included WinAVR are not compatible with newer Windows anymore. http://www.avrfreaks.net/forum/windows-81-compilation-error

2. WinAVR doesn't support ATMega32u2.
   Use the latest toolchain.

[tmk]

MSYS/MinGW install:
http://www.mingw.org/wiki/Getting_Started

Git for WIndows:
http://git-scm.com/download/win