What are home-brew RPGs
May RPGs are fantasy based
If you have ever discussed roleplaying games, you may have seen the expression Home-Brew used in reference to role playing games. Probably, most games have a bit of this mixed in - when you make a game your own, you are bound to make slight changes to suit your needs and preferences. Nonetheless, this expression can have different shades of meaning, all depending on the context. It could refer to specific rules, the actual imaginary setting. Or it might refer to the entire game system with all its rules. Sometimes it might even be used as a derogatory expression. I will try to give examples of the various cases in the following paragraphs.
I got this years ago - as a birthday present
If you play a classic Millenium's End Roleplaying game, then you have a preset world and background history. If you decide to deviate from this storyline (Perhaps because you decided that having aliens take over Madagascar was simply more interesting than having a radioactive Iraq...) then you have just home-brewed your game settings. This is fine and kosher since the objective is to have fun and presumably that is why you have done so. You might even be using all the original official rules.
If you add some magic
If you change or add rules
If you add your own rules or change existing ones - you are further homebrewing. If, in the aforementioned Millenium's End you add magic or psychic powers - you are homebrewing. Likewise, if you add heat seeking missiles and jetpacks to a fantasy genre you are homebrewing (potentially homebrewing your game to disaster - but that is your problem... People occasionally like fantasy because it is not science fiction and vice-versa).
Of course, you needn't be changing the world drastically for homebrewing. Suffice that you make minor changes to various rules (tweaking?) - that would be defined as homebrew.
Heroic Deeds - a Homebrew RPG
Homebrewing your own game
Sometimes, you find that the game you end up playing is completely different from the original rules - perhaps even something you designed yourself. That is the ultimate in home-brew a game your own, built to your own tastes. These tend to be relatively rules-lite and often fall to default rules as described in more official games but are often the most satisfying - if the most difficult to share with people unfamiliar to your own rules and game. Sometimes what starts as a homebrew ends up being published in one form or another and there are hundreds of such games all over the Internet - the one above being my personal favorite...
Tell me about Your HomeBrew
So what have you HomeBrewed into your own game - why not share?