I am new N900 user. I want make my N900 to pocket computer and that's why I bought it and I founded that it is still best solution on (secondhand) market for that. So I make lot of search. But answers was hard to read, follow or it was hard to know are those tips fully working. It was like insidetalk or monk latin Although I was programmed with assembly and used Linux first time in 1995 (but I didn't use it 1999-2011)

So I think that many N900 users want do these, but more or more easy information needed:
- Make _full_ backup, because if N900 get broken, they can buy secondhand N900 and continue with that there where they was when they backup last time.
- Use two or more OS versions. One for normal use and one for hacking.
- Use bluethoot devices
- Use USB Host mode
- Use normal programs like word processor, spreadsheet, presentation program, database and graphics program.

I don't know if I am only one who want to do these with N900:
- Use simple music making programs that can save in midi-file or rendered it to wav or aiff file.
- Use MIDI-USB devices in Host mode (example Midiman Midisport 2x2)
- Program and debug with assembly (in N900)
- Make 3D-models and even rendered whole 3D-landscape ( 600 Mhz is lot, compared to 8Mhz when I first time rendered with POV Ray in Atari ST )
- Use PC-emulator. I know 600 Mhz is not so much, but I have emulated win95 first time in enought fast speed in iMac 233Mhz, so I think with real assembler optimization it is possible.
- Make simple video editing. Again 600Mhz is not much, but twice more than system requirements for Final Cut 1.0 on Mac.

So where to start?

After search question comes:
- I founded Backupmenu, but do that make full back up if I install two OS?
- Should I install U-Boot or multiboot or what?
- Bluethoot keyboard doen't work at all, what is extra-reposity?
- So do I have install Open Mode Maemo for second OS in N900 to get Host Mode to work?
- Is Easy Debian only solution get some real office programs work?
- Can all these hacks work together?
- Can I put bigger eMMC inside N900, even 128Gb from Toshiba?

I hope that this thread comes good help for all users that want use N900 as pocket computer.

You can have "normal use" system with several things you want...
Repositories are extras (stable), extras-testing and extras-devel, you can check it at http://wiki.maemo.org/Repository it's pretty much similar to stable/testing/experimental in Debian.
You should install community-SSU, you choose "Stable" or "Testing", both are actually stable right now. http://wiki.maemo.org/Community_SSU
AFAIK, the only "useful" alternative operating system you can currently install on N900 is Android, you can do it installing Nitdroid.
You should install Kernel-Power for OC'ing (Reasonably for a "Normal Use").
Current Nitdroid Auto-installer will install multiboot, but in future it should work wit U-Boot, which is indeed better but you need to do it manually right now.
There are other systems which boot in N900 with low-to-none usefulness... basically you have Mer+Nemo (This is the continuation of Meego for N900), Ubuntu and Arch... also, hardware is not yet fully adapted in any of these alternative OS (In Android you can't make calls as they wont hear you, by some issue in Android sound system).
You can use blutooth keyboard if you've got installed external keyboard support package (extkbd).
If you install kernel-power, you just need to install USB hostmode Enabler (hen) app, check corresponding thread.
Easy debian lets you run a chrooted Debian partition from Maemo, and it's the only acceptable way of running in a practical way, full featured Open/LibreOffice in N900, but you still have Gnumeric and Abiword which work pretty well and have almost all features you may want as spreadsheet and text processor. You will be able to install a lot of things from Debian ARMEL Repo.
All of this "hacks" actually work together and in a "production" environment (Normal use system)...
As mobile computer, N900 actually works in a stable state, you don't really need to "hack" a lot...
For installing apps, I recommend you to install Faster application manager (fapman), and to install things from terminal you should install aptitude. Also, you should install bash and busybox-power to have an improved/featured terminal.
You may want to test more interesting stuff like 720p recording/playback.
I don't know about music programs or MIDI support but I think I've seen those around some time... you can install pykaraoke under easy debian... anyway use power search ------->
You can install gcc and other tools, but don't expect a full development environment in your N900, not all dev-packages are optified(ie, with actual files under /opt) (and so they would fill your RootFS, which is tiny (256MB)).
You can repartition your N900 internal memory (with mountpoints /home and /home/MyDocs), so you can install more things (/opt is actually under /home). You have to enable Developer mode and connect it as external drive in a Linux distro (Debian, Ubuntu, etc), and use gparted to "move" partition size. It's risky, so you should be sure you know what are you doing. Search for it again here ------> (Power Search)
I've not heard about povRay under N900, but there is Gnuplot to plot 3D functions and Data, and some other apps which work with that. Consider that even if installed something under Debian (where, I guess, you can find povRay), you won't be able to use Hardware rendering unless that program is specially built to support openGLES. I guess Blender doesn't works with easydebian, don't know... ----->
DosBox is a PC emulator where you can install a useless Windows 95, which works slow and with a wrong calibrated cursor. DosBox is very useful for DOS programs, tough... and GAMES! :P
I don't know about any video editing program available for N900, and I don't know if avidemux and/or cinelerra will work (but I doubt so)... You can install mencoder under maemo and under debian, but you know... it can take a LOT to convert a file into something else and available codecs are very restricted.

So, you should first read about N900 and Maemo 5, if you have something in mind, look for it in this forum.... ------------->

Welcome!