pydicom

DICOM file ( stands for Digital Imaging and Communications in Medicine) is the standard for the communication and management of imaging and other data related to medicine. It is used worldwide to store, exchange, and transmit medical images.
While the range of use of such formats is limited for the common user, one cannot deny their importance due to the potential of saving human lives.
pydicomis a package for working with DICOM files that is written and works solely in python.

Run this software anywhere, anytime

Due to the program being written and working in python, there are no system requirements for using pydicom per say, as it can work on any system that can work with python.
One limitation, however, is that if you intend on manipulating any pixel data, you will need to have NumPy installed.
It also goes without saying that due to the app's coding, there is no actual UI, so common users with no knowledge of python will have a difficult time using this tool.

Not an image viewer, but a data editor

Despite initial impressions, pydicom is designed to let you manipulate data elements in DICOM files with python code. While it can be used to view DICOM images, that is not its primary use, and it cannot be used as a DICOM server at all.
One of the few mentionable limitations is that pydicom can only store changed pixel data as uncompressed, despite it being able to decompress and manipulate pixel data.

A program with limited usage but useful for those who need it

pydicom is one of those apps that very few can find a use for (most probably only those working in medical or forensic fields), but those of you that do use it, you'll quickly realize how handy it can be.