Having recently passed the 500,000 user mark, this up and coming collaboration and productivity tool from software greats Fog Creek has made a splash in the world of startup developers and designers, and I'd hazard a guess that it could well be an excellent tool for translators too.
The web app in question is known as Trello. I can attest to its ability to organise and simplify a multitude of ongoing tasks with ease, as I've been using it for a few months now to plan Linguaquote, freelance and outsourced work. It replaces my use of paper, a permanently open text file (which is still in use for more temporary note-taking) and Google Tasks in full-screen 'canvas' mode, and it combines all of these various methods into one very effectively.
You start with what is known as a 'Board' and on this you write 'Cards' which are stored in 'Lists'. These cards can then be dragged and dropped between lists and boards, mirroring project progress. For example, on my 'Freelance' board I have the lists 'Jobs', 'Doing' and 'Done' and 'To invoice', each containing cards of projects at various stages. The cards can hold deadlines (keyboard shortcut 'd'), checklists and comments, and when tasks are finished they can be archived (keyboard shortcut 'c') to be searched through later. Tagging is done as with Twitter, with a hashtag, or you can use any convention you like, such as @clientX, [clientX] and so on. The search feature will return these in its results if required.
I've created a public test board for you to play with here: https://trello.com/b/hK63U05X
A useful feature for translators and project managers is collaboration. You can invite people to view and participate in your board, assign cards to them, allow them to vote on cards and leave comments. This centralises and reduces the overhead of a long email conversation between team members, a trend among tools of this kind that might one day prise business users away from email. We can but hope!
Currently there are no plans for a self-hosted version, but Fog Creek have been in business for over a decade and are well-established in their field so Trello won't be going anywhere any time soon. Recent talk of a paid version has also included assurances that all free features will remain so.
So after all of that, I would encourage you to take a look, as for myself and those I've mentioned it to so far are very taken with it as a very lightweight and flexible tool to help stay organised. It also has a nice name, which helps.
You'll find it here: https://www.trello.com, or via the Fog Creek link in the introduction.