Habitica

Habitica, formerly HabitRPG, is an online task management application run by HabitRPG, Inc. Unlike most task management programs, Habitica takes the form of a role-playing game. Habitica is an open source project.
Concept.
Habitica is a self-improvement web application with game mechanics overlaid in order to help the player keep track of and remain motivated to achieve their goals.
The game is laid out in the form of an RPG, in which the player collects items such as gold and armor to become more powerful. Rewards are achieved through maintaining real-life goals, in the form of "Habits", "Dailies," and "To-Dos".
Habits.
In Habitica, "Habits" are long-term goals which are utilized to change a person's habits. These "Habits" can be set to either 'positive' or 'negative', or both. 
For example:
If a user completes a positive Habit often, it will turn green. This signifies that they are doing a good job following their Habit. On the other hand, if a user performs a negative Habit often, it will start to turn red and do increasing damage to their health. When players accrue enough experience points, they gain a level, which restores their health.
Dailies.
Habitica uses "Dailies" to track habits that the user wants to complete in a known, scheduled, and repeatable fashion. Dailies are completed by ticking a check box: the user sets their Dailies in advance, and checks off what they have completed during their day. Completed Dailies give the user experience and gold; Dailies that fail to be completed by the end of the day result in a loss of health.
To-Dos.
"To-Dos" are one-time tasks that can be added or deleted. When a user completes a To-Do, they gain experience. The To-Do then disappears (it can later be found under the 'Complete' To-Dos tab). Unlike Habits and Dailies, To-Dos will never cause the user to lose health: the To-Do just becomes more valuable over time (it gives more experience and gold once completed).
Role-playing aspect.
A major part of Habitica is the role-playing aspect. A role-playing game (RPG) is one in which the player takes on the role of another person or character, and Habitica uses many genre conventions from this kind of game to motivate app users. In Habitica, the user takes control of a character that they design themselves, and by forming good habits and decreasing bad ones, the user can level up and unlock new features. 
Character.
The player can build their own character (also known as an avatar) using various customization options such as hair, skin color, and shirts. The armor and swords that a player buys when equipped also provide an attribute bonus. Some of the art in Habitica is sourced from BrowserQuest.
The class system is another feature that adds complexity to the role-playing aspect of Habitica and increases the drive to form habits. Players can choose to make their avatar one of four character classes (Warrior, Mage, Rogue, or Healer), each of which has different skills, can wear different kinds of armor, and has different primary and secondary character attributes that affect gameplay.
Levels.
Depending on how well a player completes their Habits, Dailies, and To-Dos, they either gain "experience" or lose "health". When a player obtains enough experience, they gain a level, but losing all their health will cause their character to die and be set back a level. The higher the level the player is, the more features they have access to.
Currency.
When a player completes a Habit, Daily, or To-Do, they gain Gold in some amount corresponding to the difficulty of the task. Gold can be used to buy "rewards" - which can either be user-defined, real life rewards, or else equipment that can give boosts in-game. 
Pets and mounts.
When checking off items, sometimes the player will receive an item. The items that can be found in Habitica are eggs, color potions, and food. The player can combine these to collect a set of 90 pets, which they can display beside their avatar, and 90 mounts, which their avatar can ride. Additional pets and mounts can be obtained during special events and by completing quests.
Social accountability.
Players can band together in parties to complete quests. Players can also join guilds and participate in challenges made by other players, where the person with the most consistency in performing a task wins an achievement. Players can compete with friends and strangers, as well as collaborate and focus on accountability. In parties and guilds, as well as in the community-wide Tavern, players can communicate with one another via chat.
Seasonal events.
There are four seasonal events called Grand Galas that happen each year in Habitica. Past Galas have involved new quests, special items such as limited edition equipment and avatar customization options, and bosses for the whole community to fight together. Other holidays, such as Valentine's Day and April Fools' Day, are also celebrated.
Mobile application.
An official mobile application named Habitica is available for the Android and iOS operating systems. These mobile applications are replacements for the deprecated mobile apps named HabitRPG, which were released as promised after the $25,000 Kickstarter fund goal was reached.
Reception.
In reviewing the site, Alan Henry wrote for Lifehacker that "while it doesn’t offer the advanced features that many other to-do apps have, it’s certainly a blast to use, and really addictive". Kelsey Adams wrote for CNET that Habitica (then known as HabitRPG) 'had [her] at RPG', and describes 'how much more compelling a game can be than reality to those of us whose brains are bent that way'.
History.
Tyler Renelle originally created HabitRPG to help with his own habits, having been inspired by the self-help books "The Power of Habit" and "The Now Habit". The earliest version of HabitRPG was a Google Docs spreadsheet with color-coded cell formulae.
As the community of HabitRPG users grew, Renelle reached out to Siena Leslie and Vicky Hsu. Leslie and Hsu became cofounders of HabitRPG, Inc., which was formally incorporated as a company in 2014.
On July 31, 2015, the website and apps were renamed to Habitica, after the land where players’ adventures take place. The change was made because some users found the name HabitRPG confusing or difficult to remember. The company name remained HabitRPG, Inc.
Community.
In addition to participating in the website and apps’ social aspects, the community has been involved in helping with and improving Habitica.
Contributors.
Community volunteers contribute to Habitica in various ways, such as by creating pixel art, translating text, creating music and sound effects, writing blog posts to promote Habitica, editing the wiki, resolving bugs, implementing new features, and answering new users’ questions.
Kickstarter.
Starting on January 11, 2013, Renelle started a campaign on fund-raising site Kickstarter to improve development of the application with a goal of $25,000. The goal was surpassed: $41,191 was raised by a total of 2,817 people.
API.
Habitica's application programming interface (API) allows programmers to create third-party applications, extensions, and other tools that interface with Habitica.