I never travel without my diary. One should always have something sensational to read in the train.

Jane McGonigal tells us why games make us happy:

1. There is a defined goal to achieve which provides you with a sense of purpose.
2. There are rules you have to follow that are known in advance.
3. There is a feedback system that instantaneous allows you to determine you current state of play.
4. And finally you are voluntary participating: You accept the goal and the rules.

Source:

Every team should have their own space within the wiki as a tool of collaboration. You may use the Doctypes for Agile Planning to structure your work in iterations. These iteration documents and all subordinate documents you attach to it, are also records that do not have to be updated. There are also documents for retrospectives to support you in your process of continuous improvement.

The difference is that this space and its document is organized by a team of workers that are collectively responsible to keep this a place where you can store and find information easily. The developer diary is written by a single developer. Others may read, but do not edit.

• Diary: Written by me, used by me. Others may read it.
• Team Space: Written by us, used by us. Others may read it.

A blog is a sequence of articles you publish to have them read by others. You probably want to get in contact with your readers though comments and discussion on the topics you have written about.

A developer diary on the other side, while not strictly private, is not meant to be discussed. Team members may talk to you over lunch about interesting bits or may even answer questions you have raised, but this is not its main concern. It is the developers log of events, a tool to improve and reflect about the professional goals.

While you may use a diary to log tasks, a issue management system, like JIRA, is probably a more convenient place to organize them. Especially if you are not working on them on your own and if you need some source of information for your release notes.

A diary is not a tool to organize your work for a project. It is a tool to organize yourself: the goals you want to reach and identify the parts you want to improve to get more of the things done you are most interested in.

A personal diary is a private affair. You write your most personal thoughts in it to reflect and overcome personal difficult situations. You usually do not want to share information on this level of privacy with your colleges. Keep these two things separate. A developer's diary is something you do not care to keep secret. On the opposite: You want to share but do not want to be taken responsible for information that may be delusive, not up-to-date or plain wrong.

Sending status updates to your team members via User Status Updates (a Twitter-like messaging system inside Confluence) or HipChat is a very helpful tool to synch your collaborative work. Some teams use these updates to prepare themselves for their daily stand-up.

Diary entries may also be used for daily stand-up preparation, but are certainly no tool to make status updates quickly. Team members may none-the-less access the diaries of the colleagues to update themselves by these discoveries.

A diary may by mistake stress the personal emphasis of a diary. A journal is also a log of events but by definition does not need to be maintained on a daily fashion.

So it is mostly a matter of taste to call this tool 'Journal' or 'Diary'.

A codelog is often very similar to a developer diary. It may stress on code snippets or technical solutions.