Hi,
Yes, Softing is worth looking at, as well as http://www.unified-automation.com/.
If you’re familiar with Java, and are using the Ignition gateway anyhow for the siemens driver, you might also consider writing a small module for Ignition that simply exposes the data you want over a Servlet (http response). But, if you’re trying to build a more flexible product that can connect to any UA server, definitely check out those two companies for C/C++ SDKs.
Regards,