In the Wizardry series of games, a character can assume a Good alignment. A character of Good alignment has access to certain weapons and classes, but is restricted to enter certain classes, use certain weapons, and cooperate with player characters of opposite alignment.
The opposite alignment of Good is Evil.
Good-aligned characters, normally, are merciful upon enemies that do not mean any harm to them. Usually, in game terms, this applies to friendly monsters, or those to which the character has a choice to fight or leave them. Keeping the alignment requires characters to leave the friendly monsters; otherwise, the character changes alignment and becomes Evil.
Good-aligned characters are allowed, and also restricted, access to certain character classes. A Good-aligned character cannot become a Thief or Ninja during character creation; instead, they can access most other classes including the Good-exclusive class, the Lord. Evil Thieves or Ninjas can change their alignment into Good, so eventually a Good party can have Thieves and Ninjas.
A Good character, because of what it represents, cannot be in the same party as an Evil character while entering the dungeon of the current scenario. However, a Good character and an Evil character (or a combination of both) can be in the same group if they meet inside the dungeon.
Finally, Good characters are forbidden (or merely not recommended) to equip certain items they find upon the dungeon. These items often have names implying their purpose (Evil weapons, for example). Their equipping may imply a change of alignment, and possible repercussions upon returning to town.
Duhan Saga (Wizardry: Tales of the Forsaken Land) Edit
In this series of games, the alignment system acquires gains an improvement over the original mechanics. While the characters still may change their alignment by fighting (or leaving) friendly monsters, the choice of Good or Evil upon the main character and his allies affect much more.
If the main character is Good-aligned, one of the beginning NPCs (Kyo) will have its alignment changed into Good (in fact, it is assumed Kyo's natural alignment is Good), and the rest of the beginning NPCs will have compatible alignments.
Characters with Good alignments will receive different natures than their Evil or Neutral racial counterparts. As well, Good-aligned characters will gain greater Trust with their main character when s/he makes positive comments and choices. The opposite effect will happen with a negative comment or choice.