The following is a list of alignments that fall under the term "Independent".
Survivor - Easily the most popular Independent used. Survivor wins if it can Survive until the end of the game. For balance reasons, it's advised not to give Survivor's any form of Night Kill immunity or lynch immunity, as that would practically guarantee their win condition. Oftentimes a Survivor simply doesn't have a role at all.
Lyncher - A Lyncher wins by having their target lynched. The Lyncher may or may not be told the name of their target, but often is just told the flavour name rather than the username of the player they need lynched.
Unlyncher - An Unlyncher wins if their target either survives the game or is killed in the Night Phase, or anything really, as long as they are not lynched. Given this, it is advised not to give an Unlyncher any form of Night killing.
Alien - Alien is a very rare Independent that wins if it targets every player alive at the end of the game. Games including an Alien should be aware that the Alien needs to have enough chance to have a realistic shot at their win condition.
Savage - A Savage is a fairly unusual Independent in that it wins in potentially a number of ways, depending on the implementation. A Savage may win by killing a specific player, or set of players (for example, in a Fairy Tail game a Savage may win by killing every character belonging to the Fairy tail guild). It can also win by simply killing a predefined number of players. Typically, the Savage is not told the name of the player which they need to kill.
Preserver - This is essentially the mirror of Savage. It is similarly defined rather loosely, in that it can win in a number of ways depending on its implementation in the game. A Preserver can win by protecting a specific player from a kill, or a set of players for a kill (see the example provided for Savage, except instead of killing the Fairy Tail mages, it would be protecting them and causing a kill to fail as a result), or by simply protecting a number of players from a kill. One thing to note is that a failed kill should only count if the kill would otherwise be successful without the Preserver's intervention, so using kill immunity roles should be reconsidered if using a Preserver. Unlike the Savage, Preserver's can be told which player(s) they need to protect.