I want to be able to run a program that copies a directory structure with all files from A to B. Later when files are added to A, I want the program to update B so that would be incremental. Incremental file backup software doesn't look like what I want because file backup software creates a single file and puts a copy of all the source files in it like when you backup a partition. I just want a directory structure and all its files copied. That's it. I've been googling for file copy software but I haven't found one that looks good. It doesn't need to be elaborate with tons of options either - just reliable. Can anyone recommend something? Thanks.

You can use rsync or robocopy. Depending no the OS, there may be other options, but both are very powerful

FreeFileSync or FastCopy.

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Sabo Computer Repairs & Data Recovery

Unstoppable Copier by Roadkill. Incremental updates are done using batch mode.

I thought of something that I didn't make clear. Can these programs only keep files in sync / do incremental updates on folders that these programs copied to begin with or will they also work on folders that had data to start with? For example, suppose I have 2 drives with identical data and one of them will be the main drive and one will be the backup. From this point on, the main drive will receive new files. Can I now set up the software, for the first time, to keep the backup drive identical? I wasn't sure if it made a difference if the drives had data to start with.

I think the answers are yes and yes. At least for Unstopable Copier.

As an alternative you could run a raid 1 mirror setup, depending on your hardware of course.

can personally vouch for DriveClone, it does make identical copies of your drive and is bootable to said drive.

I like SynchronizeIt! from Grigsoft. Streamlined interface, with enough options for a good customization ; the main reason why I started using it years ago is that I was looking for a software that would preserve all timestamps when copying files, including folders' timestamps : SynchronizeIt! 3.5 does this by default, and is one of the very few Windows file copy tools with this behaviour. Robocopy can do it too with the /DCOPY:T switch. I use both, Robocopy is perfect for copying or updating a whole arborescence, but if there's a need to visualize things and uncheck many files, I use SynchronizeIt!. TotalCommander and WinMerge can also compare two arborescences and copy missing files, but they don't preserve all timestamps and have no such option. FastCopy does preserve all the timestamps, but the interface is stripped, it doesn't display the files which are being copied, basically it works just like Robocopy with a very simple GUI (although I don't know if it actually uses Robocopy “under the hood”) ; it also has the reputation of being faster than other GUI-based file copy tools (according to this comparative test for instance). Most of these tools are not automated, they have to be run manually, or a planned task has to be created for them to operate at regular intervals. If you want a fully automated and constant mirroring of one drive to another, then a RAID 1 setup may be the most practical. But a real backup drive shouldn't be connected to the active computer constantly, so if you want to do this for the sake of convenience, you should still have another drive as a backup, which will be connected once a day or once a week (depending on how often and/or how extensively you modify or add files), and otherwise be stored in another place, ideally not in your home (at work, at a friend's place, in your nuclear shelter...), thus protecting you against viruses, electrical problems, flood, theft, divine wrath, angry ex-girlfriend...

SynchronizeIt! has one bug though, which I discovered : it systematically corrupts files with the “sparse” attribute (some downloading softwares automatically create sparse files, unbeknownst to the user), which get truncated after exactly 25000 bytes (the copied files have the same size but are filled with 00s beyond that point, and the copy speed is abnormally fast, like a 1GB video copied in a split second). In October 2015, I reported this issue to the author (actually it was the second time I reported it : first time was in 2010, and at the time I had no explanation...), who provided me with a fixed version, but for an unknown reason he hasn't released it publicly, the version available for download is still the old one, which has this bug (I asked the author recently why, but had no reply). If someone is interested, I can provide the fixed version by private message.