I have checked license details for dependencies listed on https://github.com/open-telemetry/opentelemetry-cpp/blob/main/docs/dependencies.md and to my surprise I found that some of them uses GNU GPL License. This means that anyone who would use this library in his proprietary closed-source app would have to release its source code.

After closer look I realized that information on that page are not fully correct. GNU Standard C++ library is licensed on GNU GPL with special exception for compiled code, so OTLP libs compiled with WITH_STL cmake option would be fine for proprietary apps: https://gcc.gnu.org/onlinedocs/libstdc++/faq.html#faq.license.what

I am worried about nostd::span, which you copied from libstdc++. Linked page also mentions GNU GPL, but in source code you have Apache 2.0. That page also mentions possible fallback to gsl::span, but as a fallback when WITH_STL is used and compiler with C++ below C++20 is used.

Please clarify these licensing issues. For now it seems that the safest way for proprietary apps is to compile OTLP libs with WITH_STL enabled and GSL libs in order to avoid possible problems with nostd::span.