Here you can download the package. A free version and a pro version is available as well as a beta version.
If you are interested in the differences between the free and the pro version, take a look at this page.

The changelog can be found here

Pro Version

If you have purchased the pro version of the package, enter the invoice number if you bought it through the Unity Asset Store or the or the serial number (which you should have received in an email) if you have bought it on this site.
After you have submitted the form, the download button for the pro version will become enabled. Note that it might take some time to load. Please be patient.

Free Version

Free version of the project. Slightly more limited than the pro version, but still very powerful. Go ahead and try it out!
Includes several example scenes showing how to use the system.

Download (version: 4.2.9, last updated: 15 Nov 2019 (3 days ago))

Pro Version

Pro version with more features than the free version. Includes among other things automatic navmesh calculation, specialized path types and layered grid graphs. See the free vs pro comparison page for more info about the differences.

You can find the changelog here

Requires Pro (version: 4.2.9, last updated: 15 Nov 2019 (3 days ago))

4.3 Beta (pro)

This beta release includes rewrites of some systems to use the Burst compiler for significantly improved performance. In particular the local avoidance and grid graph scanning now use the Burst compiler. Take a look at the changelog here.

This beta requires Unity 2019.3.0b7 or higher as well as some additional dependencies. Please read the installation instructions.

You can find the documentation here.

Requires Pro (version: 4.3.10, last updated: 11 Nov 2019 (1 weeks ago))

The A* Pathfinding Project works with Unity 2017.4 LTS and up.