Hi Yalpe, I am sure that a quick Google search will find you an enormous amount of info and free software for to-do lists, but here is my experience. There is a huge range of needs from a student through to a senior executive and you will not find one system that fits everyone's needs. Executives have sectretaries to look after their to-do lists, but that would probably be out of the question for you (certainly it is for me!!).
Although GTD, 7 Habits etc tend to decry to-do lists as outmoded, they are actually very efficient tools for daily work. Nobody expects to sort out their life's purpose and meaning on a scrappy to-do list, but for keeping control of the next few hours they are hard to beat. Scott Young (a member here) wrote about this recently, see
Scott H Young » Daily To-Do Lists
I have tried various software solutions from Word or NotePad through to freeware custom software, but I find that I finish up printing the list on a daily basis anyway. Perhaps it is an age thing, but I am still more comfortable with seeing a bit of paper on my desk with the to-do list. It gives a great deal of satisfaction to be able to draw a thick red line through a completed item, and when you get to mid-afternoon and see that 7 of your 10items are already crossed out it helps to motivate as well.
While I believe to-do lists are great for daily work, there is a need for longer term planning that does not go well with to-do lists. Here I am talking of your major goals - the life's purpose and meaning stuff. For this category the 7 Habits and GTD methods are great and you can get those books cheaply in paperback or from a library. The Simpleology system looks to me to be very similar to GTD (I suppose the GTD enthusiasts will roast me for saying that) and it provides some useful templates. Note that the first Simplology course is free. Some of the first few lessons are rather cheesy, but it quickly gets down to the nitty-gritty stuff.