When Adabas was first released (1973,1974) the only way to access Adabas was via Direct Calls.
ADAMINT (which stands for Adabas Macro INTerface) was released somewhere around 1975-1976. It was an adaptation of an interface developed by Shell Oil. The idea was to simplify the effort required by the programmers who only had Direct Calls to work with.
Shortly after Adamint was released, Natural 1 was made available. Natural was far easier to work with when compared with Adamint. Basically, shops quickly replaced their adamint modules with Natural. There were holdouts (shops staying with Adamint).
I do not know if Adamint is still supported; check with your local SAG rep.