Operating System Study from free OS

As long as I know, there are some famous operating system that already run on your machine. I think from all those operating system most of us still familiar with only about one or three of theme, i.e. MS Windows (and all versions), Linux (and all ditros), Mac X OS (and all versions), BSD and Unix. Sometime when we was asked to choose one of those operating system, most of us will make decision to choose an easiest and most popular operating system, although we should buy it. Some of us have a argument to choose free and open source operating system. Actually, I prefer to open source operating system, because with those open source OS we can deploy and make modification to meet our requirements. But, how about if we be bored by those famous operating system? When I tried to search from Sourceforge.net with keyword (+"Operating System"), I found some interested another free operating system. If you want not to install those alternative free operating system, you can use QEMU to run it. I have tried to run ReactOS (Windows like) on QEMU, although was ran slowly.
Based on those fact, I am wondering about how to use those alternative free and opensource operating system for use Operating System subject in undergraduate program. It will make more interesting subject if we can teach students about operating system design and algorithm based on those alternative OS as case study.
Here are some alternative free OS that I have found :

• ReactOS. This is a Windows OS like. I use it on my FC 6 with QEMU. "ReactOS aims to achieve complete binary compatibility with both applications and device drivers meant for NT and XP operating systems, by using a similar architecture and providing a complete and equivalent public interface."
• Haiku. If you want to know about BeOS, you can to run this operating system. If you want to run it on VMWare Player, you can download the Haiku test image that already provide at their site.
• eyeOS. This is a Web based operating system. Very interesting for all of you which want to learn about operating system design. eyeOS using AJAX technology, so you can develop any AJAX application on it.
  
• Syllable. This operating system is a AtheOS clone. "The goal of Syllable is to create a reliable and easy-to-use open source operating system for the home and small office user."
• AROS. This OS is developed to achieve compatibility with AmigoOS.
  
• TinyOS. If you want to develop an embedded wireless sensor device, this open source OS may be can help you.
  
• Contiki. This is another opensource OS that was developed for embedded device. "Contiki is designed for embedded systems with small amounts of memory. A typical Contiki configuration is 2 kilobytes of RAM and 40 kilobytes of ROM."
• MenuetOS. This operating system can only be ran only at x86 machine, either 32 bit or 64 bit. Nevertheless, this OS is very light.