Total Commander, by Christian Ghisler, is a tool I could never do without.
This is, basically, a file manager with two opposite vertical panes through which you can copy, move, compress files and so on. What I enjoy the most, being the old school, is that you can perform almost every task via keyboard shortcuts, thus speeding up your work.
You can mass rename files in every thinkable way, through the use of special fields or by searching/replacing parts of the names with regular expressions.
Searching files is also very fast and versatile. You can include or exclude paths and find a text within files, again using regular expressions, if you need to.
I have used this program for years now but I still discover new features quite regularly. Maybe this is because I tend to use just what I need at a particular moment in time and I hardly ever have the time to explore the documentation, but it is also true that Total Commander has a massive potential, despite being very easy to use. For example, I found out, not long ago, that you can have multiple tabs within each pane, which allows you to save various most used folders, that you can keep handy.
You can download Total Commander from Christian Ghisler’s Website.