How is it possible to get dev in multiplayer?
Cause there are servers where they have it.

where can i download?
what is it called?

Dang, do I wish I was on my Halo computer right now. I have the textfiles explaining, but that's being lazy. I'll do it myself;
What you want is called alldev and/or Dev Trainer.
Alldev can be found here:
http://hce.halomaps.org/index.cfm?fid=1099
This is just a simple program. Open it when in Halo or before you start up, doesn't matter.
Page up will turn it on, page down will turn it off. To use it, press the [~] key(The key next to your 1). This will bring up console, I forget if you have to have it in your target or not. I'll explain more later. To use cheats online (which I hope you don't in your own server to win) just type it in, except it's like this. Deathless would be cheat_deathless_player 1. (1 turns it on, 0 turns it off) I suggest using this to get the hang of it-
http://hce.halomaps.org/index.cfm?fid=2665
This can be activated whenever, like alldev. It's pretty self-explanatory. When in the console [~], just press F1-12 and it will type in the cheat, and also show what you did in the chat box. The 'server' will say it. To turn it off, you can just press that same key again, and it will auto-matically type the same thing in, except instead of 1, it will do 0, to turn off said cheat. Xfire me at odx999 if you want to know more.

Thanks ODX.

And selenic, i was being specific.
Dont be so rude.

I suggest using this to get the hang of it-
http://hce.halomaps.org/index.cfm?fid=2665

This program has two of the commands you just told us about, but I would recommend NOT pushing them over and over again, because you will have so many weapons/vehicles/powerups you'll exception out.

He was also being obvious. Though I do somewhat enjoy giving people instructions of how to cheat...er.

My milkshake brings all the boys to the yard, damn right, theyre better then yours