Let me side-step some gratuitous comments about the apparent lack of control in your environment. My apologies for the situation; try to reign those cowboys in :)
Definitely look at Rancid for your networking needs. You can monitor changes to configurations. Additional integration will let you automate backups upon detection of configuration changes based on Syslog messages or SNMP trap notifications.
For Linux, consider forcing admins to access hosts through a logging portal (like an SSH jump with a
ForceCommand that wraps
script(1) before connecting to a destination host). Venerable tools like Tripwire can log inappropriate changes made to system files.
For Windows, check out the pretty software from ObserveIT, which can do host-based monitoring of interactive sessions.
Given that you seem to have already had some face-blowing-up going on, I strongly encourage you to foster a culture of responsibility about this (a "soft" control / policies). Some admins do behave like cowboys, but surely most understand that undocumented. unannounced changes lead to problems. Establish work windows, production blackouts, change notifications, etc.
This are simply smart practices, which they and customers will come to appreciate; the admins because they'll be able to find out when they shoot themselves in the foot more easily and customers because they'll feel more aware of what's going on.