Is it copyright infringement to make a game based off another game, so long as no monetary gain is involved?
There’s an old RTS I have, that I grew up on, and I’ve always wanted to create a fan sequel. Well, I’ve throw a few models together and I’m just getting a concept together, and then bam, it hits me:
This could be copyright infringement!
The topic itself didn’t exactly fit in with anything in the game engine section, so I posted it here. This would probably be better off asked in a place like ModDB or Fileplanet, but what the hey, no harm in asking here before hand.
Is it copyright infringement to make a game based off another game, so long as no monetary gain is involved?
Copyright infringement has nothing to do with monetary gain. If you rip a cd, make 1000 copies and give that away free to people out of the goodness of your own heart do you think you are not infringing the rights holder copyright ?
Well…
I’d have bet money that would have been at least PART of it 
Anything else anyone can tell me?
i think it has less to do with copyrights and more to do with trademarks. copyright infringement would be if you made pirated copies of the game. violating a trademark or something would be including the game’s name, logo, etc. in your own game.
basically, if you just clone the gameplay style without references to the original game, you shouldnt have problems.
As long as you make the game on your own from scratch, you dont have to fear about copyrights.
Alsoi’ve heard that the fan made games dont violate copyright law, unless it is commercial.
btw if you dont mind, what’s the name of the RTS game that you wish to sequel? mgs?
Copyright != Trademark
If you ever heared the term “licensing” you´ll find out what the latter is.
e.g. THQ pays to Gameshop to be allowed to make Warhammer Games, although they would not violate any copyrights by doing so.
if you want to produce a Super Mario Doll, you got to pay license fees to Nintendo, although you make them all yourself.
…
Technically, yes, it is illegal, but they are unlikely to sue you as it falls into the category of fan art.
Unless, of course you happen to be making a lot of money from it, then it would be worth their while.
But don’t ask me, ask your legal adviser.
Ask Nintendo, who sued the crap out of fanboys with only good non-profit intentions IIRC. 
It´s best to check this stuff prior of starting, like contacting the TM/(C) holder and ask for a written permission, or a contract where you declare to do it non-profit. Better save than sorry.