Keep A Journal With This Dedicated Windows Tool [1]
There are many Personal Information Manager (PIM) tools around, but I've never encountered one before that's specifically designed to help you keep a daily journal. OK, to be fair, I probably haven't been looking very hard. But here's a program that does it, and it's free.
Red Notebook is a 24 MB download from http://portableapps.com/apps/office/rednotebook_portable [3] if you want the portable version (which is the one you might as well try, because it's the easiest option). The program is malware-free according to VirusTotal and Web of Trust.
Once you've downloaded it and run the installer, click into the folder that it creates and then click on the application to run it. You can then start creating your journal, or viewing previous entries, by clicking on the dates in the calendar.
There's a full search facility, and a word cloud, and you can add hashtags and formatting to your text. Your journal gets saved in a folder as a series of files, so it's easy to keep a backup simply by copying the contents of that folder elsewhere. Or zip it into a single file if you prefer.
Whether you want to keep a daily journal for personal reasons, or you need to keep track of all the work you do, Red Notebook is simple to use and costs nothing. And if you don't like it, removing the portable version from your PC takes nothing more than deleting the folder containing the program.