zOS Assembler - APIs

While not being an exhaustive list nor is the support of additional APIs a problem, the following are those APIs with which we have most frequently been confronted:

CS VTAM native
This API is used by us to support all of the earlier SNA LU protocols, most commonly LU0, LU1 and LU2. The protocols are supported in both primary LU and secondary LU (typically terminal emulation) roles and in either contention or flip/flop modes of the necessary half duplex protocol.
Supports the LU6.2 protocol, most commonly used to interface with CICS (see OTMA for IMS interfaces). This simplified API requires that the devloper has a knowledge of the underlying SNA flows if efficient program to program communication is to be established.
This sockets-like API is not recommended for new projects with more than a handful of connections. The API actually creates a USS environment in the background and feeds into the callable services API below. Far better to invoke that API directly. We continue to provide support for customers with this API.
CS TCPIP USS callable services
This API expects tasks to have been dubbed as USS processes but then provides an efficient VTAM native API like interface to TCPIP networks.
We have experience with the Open Transaction Manager Access (OTMA) client which provides efficient device independent access to IMS.
Tivoli NetView
While not an access method API, Tivoli NetView provides APIs to improve its operational interface through customization using assembler, REXX and/or other high level languages. See the REXX and NetView pages for details.