Ada

Ada programs can be compiled by a FLOSS compiler, GNAT, which is integrated into the gcc compiler suite. Ada Core Technologies offers support for GNAT.

SPARK is a sub+superset of Ada for developing provable programs. Programs written in SPARK can be compiled by a standard Ada compiler, including GNAT (GPL). They can also be processed by SPARK tools developed by Praxis that were released as open source software (GPL license) in June 2009.