WinMD5Checksum

WinMD5Checksum is an intuitive tool that enables you to calculate the MD5 and SHA256 signatures of files, as well as to compare any two hashes to figure out if the associated files have matching content or not.

Simple interface for bulk operations

It's packed in a user-friendly interface made from a large window with a plain appearance and neatly structured layout, where you can open as many files as you want, thanks to the fact that batch processing is supported.
We've noticed some slight inconveniences here. When using the file browser, you can select and open only one file at a time. Multiple selected items can be dropped in the main window from your file explorer, though.

Calculate and compare MD5 and SHA256 hashes

If you want to just calculate the MD5 and SHA256 signatures, simply start the processing start. Otherwise, you can type or paste secondary MD5 or SHA256 hashes to match them against the files.
This information can be saved by creating an .md5 file in any specified directory on the computer. Moreover, you can make the frame stay on top of other windows. Command lines are supported for skilled users.

No setup necessary, besides .NET Framework

The program's not wrapped in a setup pack. However, it's not entirely portable, since it needs .NET Framework. You can drop the downloaded files in a preferred location on the computer or copy them to a removable storage unit to run WinMD5Checksum on any PC with Microsoft's platform installed.
Just keep in mind that it auto-creates and updates a log file on exit with errors and other details about its activity, so make sure you're not launching it from a write-protected device. At least it doesn't add new entries to the system registry, unlike many installers.

Conclusion

WinMD5Checksum may be a little rough around the edges, but it offers an effective solution for calculating and comparing the MD5 and SHA256 hashes of files in batch mode. CPU and RAM usage was minimal in our tests.