Here's some broad categories of anti-poopsocking features.
The game detects that the player has been going for a long time or is playing into the wee hours and advises him to wrap it up and go to bed or grab some fresh air. This may be intended in all seriousness or is just a fun fourth-wall-breaking Easter egg for the player to stumble upon. Not likely to be effective unless they are backed up with more substantial time limiters.
A stamina bar that gets used up a little with many actions you take. When empty you cannot do those actions until the energy grows back in real-time. Very popular with Zynga games like FarmVille. Easy for the player to understand, simple and effective, but also quite limited in comparison to methods like Harvesting.
This method includes other types of automatically replenishing resources such as oil in Airport City or coins in fruit machine games. Other games do this with the health mechanic, where the player needs to leave his character out of combat or even has to put him to bed at the Trauma Inn until he gets the chance to revive.
A plot of farmland, house, shop or other item that is inert until a point in the future when you can use it to get resources. Once you do that it goes inert again. Farmland yields crops, businesses disgorge profits, houses pay their taxes and so on.
Unlike Energy the player usually has to do something to get the resource, such as click on each unit to make it cough up the goods. Sometimes the player also has to prepare the unit before it will start growing the resource, for example preparing the ground and planting the crops he wants to harvest later. If he waits too long to harvest the resource may go bad, which happens a lot in farming games where the crops eventually rot in the fields and become valueless. This is a great way to get the player to come back to the game regularly – if he lets the game sit unplayed for too long he could lose a lot of expensive plants!
Harvesting is much more versatile than energy in that you can often set how long you'd like the resource to grow so it's ready when you are. Harvesting can take up a lot of the player's time and it's often a main part of the gameplay.
Includes letting the player character learn skills faster while the player is logged off, or leaving the PC to grind away at some boring task such as cooking or making potions and benefiting from the results on returning to find them done.
Set times of the day in which the game is limited or outright unplayable. Examples of the former include games where important NPCs will only be around help the player at certain times of the day, which is synchronised with real-world time (eg. Animal Crossing). Latter examples include server shutdowns imposed by governments, eg. South Korea's gaming curfew.
Sometimes things just happen in your game whether you're playing it or not – your Tamagotchi gets hungry, zombies break through your defenses and start destroying your crops, another player invades your kingdom – events that are sufficiently rare so as to not force you to remain playing, but do get you to come back from time to time and clean these messes up before they get worse.
Some games are by their nature almost impossible to play endlessly. For example, a turn-based multiplayer game where you might be waiting hours for your opponent to act, or a Wiimote or Kinect game where playing for a long time would just tire you out.
Many games combine the above methods. For example, many Zynga -Ville games require the player to spend a unit of energy every time he harvests a plot of land.
As mentioned on the main page, many anti-poopsocking methods are not just about pushing players into taking breaks from gaming, they are about regulating their time, persuading them to return and continue playing again and again. By pushing the player away then attracting him back the hope is to give the game a long-term appeal while not wearing him out too soon.
Every single method mentioned above (with the probable exception of Dropping Hints, which isn't terribly effective anyway) can be used to attract players back to the game as much as push them away from it.