graeme_p - 10:07 am on Nov 13, 2012 (gmt 0)
MacOS X uses a lot of open source components: Darwin (BSD/Mach hybrid), bash, webkit (derived from KDE's KHTML), Python, Sqlite etc. Even the proprietary API is based on an open standard (OpenStep) that has an Open Source implementation (GnuStep). If you use a subset of the API, you can write software that can compile on both MacOS/iOS and Linux or BSD. Interesting that Sony has funded GNUStep.
Android is open source itself, and uses a lot of stuff from other open source projects (a fork of the Linux kernel, Webkit, GNU utilities, and probably more).
If I open a terminal on MacOS or Android, its just like Linux.