I would argue linux is deserving of a place among that list (despite the many distributions I will lump it together). Maybe BSD and some of the others would fall under other but linux still makes that list in my estimation.
Anyhow whatever does the job I need it to do is what I use and what I install for clients- typically this means a version of XP (still a corporate standard and a bit cheaper/more commonly existing than corporate grade 7), a version of XBMC (people really seem to have got into media players of late), a version of debian (servers and such although I have been meaning to look at centOS more) or linux mint (desktops) or a version of opensuse (mainly as it winds into selinux well- people wanting secure laptops and such for banking and travelling). Outside of those that like toys, are lovingly referred to as the coloured pencil departments and/or stuff like ipads (they do have nice email and a halfway acceptable browser) though nobody has really gone for apple- if you are going to lump yourself with incompatible software or just need an OS that does a browser and VNC/RDP you might as well get one you do not have to pay for (both in software and limited selection of hardware).
After this it seems even I have got roped into virtualisation (next step- evaluating proxmox for corporate use) which makes this even more meaningless/goes towards reducing OS to an application/library/API level which for my money can not happen soon enough.
Windows 7 (64bit) at home (for gaming and developing in .net).
Mac OS X 10.5.8 at work (because that's what they use here).
Ubuntu 11.10 on my laptop (because it's an old laptop, and ubuntu is pretty lightweight).
In the TROOP database, select which enemy you wish to have join the fight and insert them into the scene like you would any other enemy. Right click them and select "appear halfway". Then down below in the events panel, set a conditional event for when your main enemy hits a specific %hp and select the "Enemy Appear..." command on page 3. Then select the enemy you wish to appear!