IBM PS/2 Model 57 Linux is a small Linux distribution for the IBM PS/2 Model 57 (or any other 32-bit x86 PC). It can run fine even on a FPU-less 80386 with 4 megabytes of RAM. It is based on a Linux 2.4 kernel and uClibc. It is mostly meant as an install disk that installs a system on which you have to compile your own software. Providing the standard library shared files or compiling binaries statically is your own responsibility. This avoids the hassle of getting something to run. Installation is done with a simple installer and the installation media is just two floppy disks.
The PSXSDK is a free and open source software development kit that enables anyone with C programming knowledge to make programs and games for Sony's PlayStation console. Everything was either written from scratch or based on already available open source resources. It is thus free from any proprietary code and fully legal to use. The SDK is mostly geared towards a *nix environment, but is fully usable with emulation environments such as MSYS and Cygwin.