Stardew Valley is full of NPCs that you can speak to, flirt with or buy and sell from. Most of them will be found around town, although the odd person will be a bit tougher to track down. Each page will tell you their birthday, location, gifts, and heart events.
These are the NPCs eligible for marriage. Shane and Emily were added as romanceable NPCs as of update 1.1. Krobus, while not romanceable, can move in to your farm as your best friend/roommate if he is maxed out and you are unmarried.
As well as these romance options, there are a variety of other NPCs in Stardew Valley. Some are there at the beginning of the game, others arrive on certain dates, and others arrive upon the completion of a quest.
Around half of these can receive gifts and operate basically the same as romanceable NPCs with gift preferences and heart events, they just will not marry you at the end of it. The other half exist in the game for specific quest reasons, and will not accept gifts and so do not have a heart rating. Check out the differences below/
These NPCs are all eligible to receive gifts in order to boost their friendship. While there are certain Universal gifts which all (or at least, most) villagers feel the same way about, each villager has their own preferences. Click on each name to see which gifts to give them, and use the Gifts page to see which gifts fall into which Universal category.
These NPCs cannot receive gifts. That may be because they are only linked to certain quests, accept other donations (to the Museum, for example), or are there to give out rewards. Click on them to see what each of them does in the game.