It is the third most popular of the Ethereum clients, behind
geth (the go client) and Parity (the rust client). The code is
exceptionally portable and has been used successfully on a very
broad range of operating systems and hardware.

We are in the process of re-licensing the codebase from the
copyleft GPLv3 license to the permissive Apache 2.0 licence,
to enable Ethereum to be used as broadly as possible. There is
a long-form article - "Ethereum Everywhere" - which talks about
the rationale for the change and the history leading up to this
proposed change of licensing.