GT.M
From VistApedia
GT.M is an implementation of ANSII standardsMUMPS from Fidelity Information Systems. It is widely used in the banking world, and in addition, it will run VA VistA. At present the only well known alternative is Cache
Fidelity is the maintainer of GT.M. In addition to their open source version, they provide nonfree software that runs on the Oracle Solaris Operating System, running on the Sun SPARC line of high performance servers. They also offer service contracts and training to open source users.
Extensive documentation from Fidelity is here. See also GT.M Programmer's Guide.
GT.M can support VistA. The portability layer of the Kernel is known to work with GT.M on VMS, Solaris, and Linux Operating System.