Use a build of OpenJDK provided by the Adoptium project.
Or, for specific needs, consider any of several other vendors discussed below.
New release cadence and policies
You should know that Oracle and the Java community have changed to a new release cadence. Major production-quality releases will come on schedule every six months. Every three years a release will be designated as a Long-Term Support (LTS) version where the community will strive to back-port vital fixes and security patches, but no new features, for a number of years.
Java 11 is current
As of 2021-06, Java 11 is the current designated LTS version, as is Java 8. The latest and greatest version is Java 16. Later, in 2021-09, Java 17 should arrive, and may be designated as LTS.
All implementations I know of for the AMD/Intel 64-bit market are based on the OpenJDK project. The OpenJDK source code is open-source and available freely without cost via a Mercurial repository originally, and now on GitHub. Several vendors provide releases built on this codebase.
Regarding ARM chips, Java 16 is currently available for Windows/AArch64. Java 17 will be available for macOS/AArch64 (Apple Silicon), with early-access builds available now.
Note that using OpenJDK does not include rights to use the “Java” brand owned by Oracle; for that a vendor must (a) pass rigorous testing for compliance with Java specifications and (b) meet Oracle’s licensing terms.
Be aware that Oracle has changed their terms for use of their Oracle JDK product, no longer allowing use in production free-of-cost. Discussed here.
Also, be aware that Oracle has declared their intent to bring their own branded JDK into feature parity with OpenJDK. Oracle has even gone as far as to donate some formerly commercial parts to OpenJDK, including Flight Recorder and Mission Control.
Read Java Is Still Free
For both an overview and the gory details of the new cadence and terms of Java releases, read the very important document, Java Is Still Free. Written by key members of the Java community to clear up the recent changes.
Several releases for you
To answer your needs, I know of several sources for a release built on OpenJDK 11 available free-of-cost with deployment rights available for download to Mac, Linux, and Windows machines. (Listed in arbitrary order.)
Guide to obtaining Java 11 implementation
Here is a flowchart that might help you in choosing a source for obtaining Java. Note this chart may be incorrect or incomplete. And of course you are responsible for studying and obeying the license and terms for any software you obtain.