Linux i686 (32-bit) is a Unix-like and mostly POSIX-compliant computer operating system (OS) assembled under the model of free and open-source software development and distribution. Using host OS (Mac OS X or Linux 32-bit) you can build native application for Linux i686 platform.
For more detailed information please visit vendor site.
Examples are listed from Linux i686 development platform repository:
; Latest stable version [env:latest_stable] platform = linux_i686 ; Custom stable version [env:custom_stable] platform = firstname.lastname@example.org
[env:upstream_develop] platform = https://github.com/platformio/platform-linux_i686.git
GCC Toolchain for Linux i686 machines