"Someone said, failing to plan is planning to fail."
To start with, I am not one to spend $50-$100 per day that I am going to be in Germany on airfare, then arrive there and say, "Where do I want to go?" In fact, I already have a long list of things I want to see in Germany, and another list of things I've already seen but want to show someone else, so the first thing I do when I start to plan is to decide where on those lists I am going to go and what I am going to see. I don't just decide to go to somewhere and then ask myself what I want to see.
So my plan starts with the places to which I am going, the towns I am going to visit and what I am going to do there. So, yes, in that way I am regimented. If I want to see one thing in a town, and I go there for one day to see it, then that's on my agenda for that day. But plenty of times, I have planned 3, 4, maybe more days in a town, and I have a list of things to do there, and some days it is just "hanging out". Then I do whatever I feel like doing on that day.
I always have a schedule of where I am going to spend each night of my visit. That way I can make reservations early for a place where I want to stay. Early in my travels I tried going without reservation, just coming into a town and finding a place to stay. That didn't work out badly, but it wasn't optimal, either. In one town, I arrived a day early and did have a reservation for the following night , but I decided to try the TI option. As it turned out, the reserved place had the room vacant for the first night. The place they sent me to was OK; it was not as convenient as the place I had reserved to the following night, and it was a little more expensive, but it worked. I realized then that the TI doesn't give you the best place remaining in town, they give you the next place on a rotating list. It pays to reserve early.
There are plenty of people out there that know how to reserve early, and when they find the best place, they don't say, "that's a good place, but I won't take it. I'll leave it for someone how arrives later." No, they take it and you get what others didn't want.
So, to get to the point, the tool I use is a spreadsheet - actually what I think Excel calls a workbook, a lot of worksheet tabs together in one file. I have a worksheet for every place where I will spend a night, with a list, including, when I'm still in the planning phase, of suitable places to stay. Then I have a worksheet for every day of travel, with schedules for trains or buses to get to where I am going. The first worksheet is an index with a link to each night of accommodations and to each day of travel. The second sheet is my itinerary, with similar links.