Today in the series "How to do XYZ with software?":

How to manage time?

I have no idea. Well, at least I can tell you how I use computers to help me in managing my time. But beware: people tend to be(have) very different in self-management, and time-management is an essential part of self-management.

After having used little notebooks as calendar as well as to-do-list for some time, I tried to use the calendar from my mobile phone, then from a Psion hand-held (it was a 3c model, like this one) and even a Palm (a very, very, old model, I didn't even find it with Google). It wasn't very satisfying. The best experience I had was with the desktop application Ximian Evolution, which is a Linux-clone of the popular Outlook. But it wasn't "mobile". It wasn't really able to synchronise with any hand-held or mobile phone (it just pretended to be able to do so, but it was always a big mess).

Then I switched to Google Calendar. Now the data is accessible everywhere and it's much much easier to invite someone to common dates (it's even easier if your friends use Google Calendar, too - you can let others view some or all details of your calendar, if you want to). It's simple to have multiple calendars in one user interface, so you can have one calendar for your private stuff, one calendar for your work stuff (which your colleagues are allowed to see, for example) and one calendar for your organization (which is editable by the members of your organization, for example). Wonderful!
If you still want to use Outlook or Evolution - no problem, Google Calendar interoperates very well with other calendar systems (thanks to open standards).
I guess you won't need Google for this, Yahoo's calendar might be as good as Google's, but since I use an Android phone, which naturally synchronises with Google products, it's just easier for me to stick to the Google calendar I've been already using. (Well, I think it is possible to do this with Yahoo, too). The mobile phone synchronisation (for iPhone too, for example) is very satisfying. For those without smartphone, Google provides SMS (mobile phone message) reminders for free (at least in the US and Germany... and some other countries). I used the SMS reminders for a while, before I bought a smartphone, and it was useful, too.
Since a few weeks, Google integrated their todo-list a little bit with the calendar application. This doesn't satisfy me yet, but maybe it suits your needs. For me, it's better to use a to-do-list application on my Android phone (there is one for the iPhone, somewhere on the Google tasks website) and ignore the relationship between calendar and to-do-list. Undocumented feature: stand-alone tasks application from Google.

(comic licensed from Randall Munroe under a Creative Commons Attribution-NonCommercial 2.5 License)

Once I made an experiment: two weeks of time-tracking. This means, I logged everything I did for more than 10 minutes (there were about 20 categories of time-consuming actions, including "other", "sleep", "eat", "learn", "wasting time in the internet"). The application used for this purpose was android-timetracker, a wonderful app (available for free in the Android market) to do exactly this, nothing less and nothing more. The result of two weeks of careful tracking: About one hour per day was completely wasted time that I could have spent better. That's not that bad - I've had expected worse. And it's no surprise that you spent lots of time sleeping (a little less than I thought, too) and lots of time working. So the data was not that interesting that I would recommend this experiment. Maybe you're continously asking yourself "where did my time go?" and then this may be good for you.

The difficult problems in time-management come with personal goals such as "quit smoking" or "do more sports" since these goals easily get lost in daily work. There is no tool I know of to really help you with this stuff. I once tried ThinkingRock, a GTD (getting things done) application, but after a while it wasted too much of my time without actually helping me much (although it was cool at the beginning). It may help you, since it pushes you to think about building a bridge from youŕ far-future goals to do-it-now-tasks. But I prefer to do this kind of thinking within my personal notes, much more unstructured (and differently-structured) than within ThinkingRock. I could list many more tools that help don't help you getting to your goals, and I strongly believe you should better read something about the psychology of motivation instead of software tools.