Well seeing as I am the first to have triple-booted on the N9, thought I should help others. I'm not sure how many people want to know how to do it, or not, but it is good to share knowledge. I will divide this up into installing Nitdroid and Nemo. Sadly, I have only tested a tethered boot into the Moslo Bootloader for Nemo.

I TAKE NO RESPONSIBILITY FOR WHAT HAPPENS TO YOUR DEVICE. THIS IS DONE SOLELY AT YOUR OWN DISCRETION.

Nitdroid

1. Install dual-boot kernel as described here: http://forum.nitdroid.com/index.php?topic=90.0

2. Install sillyboot. Details: http://forum.nitdroid.com/index.php?topic=91.0

3.
a. Download tarball from here: http://depositfiles.com/files/ue9wxpz49
b. copy the archive to your Nokia N9.

c. execute "as root" command

tar xjvf /path_to_archive/nninedroid_ics_alpha1.tar.bz2 -C /home/

Nemo

Assuming use of Linux Host and Harmattan Flasher installed

Create a folder on your desktop eg NemoN9
Download this http://repo.pub.meego.com/home:/marq...N9.armv7hl.rpm to that folder
Using the terminal enter

cd /file/path/to/that/folder/

rpm2cpio moslo-n9-*.armv7hl.rpm | cpio -vidu

Once completed, enter

sudo flasher -k usr/share/moslo-n9/zImage-moslo -n usr/share/moslo-n9/initrd-moslo -l -b

Your N9 should then boot to a screen with green text. Wait until it says alternate rootfs exported via usb
Your pc should auto mount. (If not, run dmesg and look for sdx where x is a letter or number, eg sdb. Then run mount /dev/sdb /media/Alt_OS or you can unplug/replug USB and repeat step three until N9 is automounted)
Once mounted, run

sudo tar --numeric-owner -xf nemo-handset-armv7hl-n950-*.tar.bz2 -C /media/Alt_OS/

When extraction is complete, unmount the device
umount /media/Alt_OS

Unplug the usb and you should get an option to boot Harmattan (Vol+) and Alt OS (Vol-). Alt OS boots Nemo. Continue through to Harmattan where you will be prompted to boot an Alt OS again (Nitdroid) by pressing Vol+. If you wish to go to Harmattan. Do nothing. To get to the screen to boot nemo, you must repeat step 4 only. Once these screen says "alt rootfs exported" unplug USB and press Vol-.

Contact me via email or twitter for support

Does this also work for N950 users?

Sadly No. I attempted this initially on N950, but Nitdroid won't boot. Nemo dualboot is fine, but Nitdroid does nothing. That is what lead me to experimenting with N9

I hope that e-yes will support N950 users aswell

So I need a linux computer to do this ?
Is there any problem with Nemo ( eg sleep mode not working ,..)

can i do that with normal pc? i want nemo, nitrdroid and meego? :P

AFAIK, no, due to the way the rootfs is exported. Do like me and download a VM client such as parallels or virtual box and install ubuntu

Followed your guide but got stuck with the nemo os part.
Whenever I try to run the command
It writes a warning about bad kernel.
any suggestions?

EDIT: Managed to handle that problem, but when I'm trying to mount my N9 into the Ubuntu (using virtual box) it gets disconnected every second..

I have followed the steps but the flasher doesnt find my N9. I am using a vitrual ubuntu machine. any help on this?

Got this to work on the N950. Incidentally I took a screencast (on the desktop) as well as a video (of the device), and I was writing documentation about it; will upload for reference. I pretty much followed MFaroTusino's steps from his blog site: http://mynokiablog.com/2012/03/22/wo...tdroid-how-to/.

Device Firmware: PR 1.3
NITDroid Version: Alpha 4 (ICS)
Nemo Version: the latest releast (08.31.2012), but I later on decided to try the build which has Plasma Active on it.