We have just finalised Namecoin Core 0.18.0: https://github.com/namecoin/namecoin-core/releases/tag/nc0.18.0

This is based on the recently-released Bitcoin Core 0.18.0 and thus includes a lot of new features (e.g. improved multi-wallet support) in addition to some Namecoin-specific changes.

Important: Everyone should update as soon as possible.