pydicom is a pure python package for working with DICOM files. It was made for inspecting and modifying DICOM data in an easy "pythonic" way. The modifications can be written again to a new file.
As a pure python package, pydicom can run anywhere python runs without any other requirements, although NumPy is needed if manipulating pixel data.
pydicom is not a DICOM server, and is not primarily about viewing images. It is designed to let you manipulate data elements in DICOM files with python code.
Limitations -- the main limitation of the current version is that compressed pixel data (e.g. JPEG) cannot be altered in an intelligent way as it can for uncompressed pixels. Files can always be read and saved, but compressed pixel data cannot easily be modified.