Which SCM solutions exist for managing mainframe software?
From my own experience, these are some the typical softwares packages:


CA Endevor.
SERENA ChangeMan ZMF.
Compuware ISPW.
IBM SCLM.


All of these packages can manage, more or less out-of-the-box, anything that's stored in regular "PDS" components (a typical file structure used in z/OS).

When it comes to a company evaluating which one best fits for them, it often boils down to these criteria:


IBM SCLM is perceived as free of any license/maintenance fees (actually it's included in the z/OS license, which itself is not free). So if no dedicated budget is available, then this is often the software package that gets selected (better then no package at all). If there is a budget, then this one is often the one that doesn't make it to the shortlist.
CA Endevor has the highest install base. Its key strength, IMO, is the way that you can trace down for each executable how it has been compiled/linked using which version of which building blocks (copybooks, etc).
SERENA ChangeMan ZMF's install base is quite a bit below the one from CA Endevor. Some of its key strengths are:


the notion of "packaging" related software changes, which is at the core of it.
its capabilites to deploy softwares towards physically remote sites.

Compuware ISPW is like the "new kid in town" (as compared to the CA Endevor or SERENA ChangeMan ZMF alternative). It is commonly perceived as the solution where "any custom SCM requirements can be implemented with it, with a relatively low effort to do so".


Looking at it from an architecture standpoint, then SERENA ChangeMan ZMF and Compuware ISPW appear to have the most open architecture, which is what you'll need if you want to tune it to make it manage software components written in a 4GL language that is (what some call) more exotic, as compared to 3GL languages such as COBOL, PL/I, etc. I.e. because the software components are stored in file systems that are not stored in standard PDSs. Some examples of those languages are:


Natural (stored in ADABAS DBMS).
ADS Online (stored in IDMS DBMS).
QMF (stored in DB2 DBMS).
CA Gen (stored in "encyclopedias").
CSP (stored in VSAM file format).


Attention: having an "open architecture" is great to have it fit your custom requirements (the sky is the limit). However when it comes to upgrading to new releases, it comes with a price to get those custom requirements upgraded also.

Note: rather accidentally, during a CA Endevor training for SERENA ChangeMan ZMF experts, we discovered that CA Endevor and SERENA ChangeMan ZMF appear to have the same roots (from somewhere in the late 1980s ...). For those who are a bit familiar with both of them: go check what the functionality is of these utility programs, with similarly named names ... (you'll be shocked ...):


PGM=CONWRITE versus PGM=CMNWRITE.
PGM=CONPRINT versus PGM=SERPRINT.