The first game that set the standard for the dating sim genre was Dōkyūsei (1992), which relied more on timed events than dialogue choices.
There are many variations on this theme: high-school romances are the most common, but a dating sim may also take place in a fantasy setting and involve such challenges as defending one's girl from monsters.
One game series that often includes dating, with the goal of marriage, is the farming sim series Harvest Moon.
The subplot of dating is more focused towards choosing one of several girls or guys (dependent on the player character's gender) and offering them presents or joining them on events in the game.
The Star Ocean series of RPGs also feature dating sim elements in a similar manner.
The player must befriend and carefully build and maintain a relationship with one or more characters.