Bitcoin Core version 0.16.3 is now available from:

https://bitcoincore.org/bin/bitcoin-core-0.16.3/

For the release notes please see the git repository:

https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.16.3.md

Preferably use the above download link, not the below links to download the source tarball, as the release tarballs are generated deterministically whereas GitHub's are not.