From Wikipedia...
Action! is a procedural programming language and integrated development environment written by Clinton Parker for the Atari 8-bit family. The language, which is similar to ALGOL, compiled to high-performance code for the MOS Technologies 6502 of the Atari computers.
The assembly language source code for Action! was made available under the GNU General Public License by the author in 2015.
This requires 64tass to assemble from source.