In the folder binaries are currently found the compiled executables of iasl directly from Intel's own sources.
Since the actual iasl compiler name is the same through each new release, each version stored here is differentiated with the release date from Intel. Just download the needed binary and rename it back to iasl for using it later.
The ACPI Component Architecture project is currently hosted over at https://www.acpica.org/
The sources themselves are freely accessible at https://www.acpica.org/downloads/ as acpica-unix-YYYYMMDD.tar.gz files (Intel license).
According to Intel, their entire source code for the ACPICA project is maintained under the git version control system in a single repository.
This repository can be directly accessed via git://github.com/acpica/acpica.git
According to user acidanthera's page for MaciASL tool, to build the latest ACPI compiler we need download the (latest) source release from ACPICA.org and compile it via Terminal.app with the following command whilst in the unpacked sources folder:
CFLAGS="-mmacosx-version-min=10.7 -O3" \
LDFLAGS="-mmacosx-version-min=10.7" \
make iasl -j $(getconf _NPROCESSORS_ONLN)
The iasl binary will be later found at ./generate/unix/bin/ path where you launched the above command from. To test that it has been compiled properly, run:
./generate/unix/bin/iasl -v
An example output of the 2020-05-28 release (based on source acpica-unix-20200528.tar.gz) is:
Intel ACPI Component Architecture
ASL+ Optimizing Compiler/Disassembler version 20200528
Copyright (c) 2000 - 2020 Intel Corporation
The developers are releasing, from time to time, updates to their main tool MaciASL that includes the latest compiled binaries at the time of each release.
Should one need to (manually) update MaciASL.app binaries with latest (or previous) compiled iasl versions, one can simply go to the /MacOS/ folder of the tool and replace iasl-stable or iasl-dev with the respective versions needed.
Remember that iasl-dev is the binary that's supposed to be the latest available, so that compatibility is kept with iasl-stable and iasl-legacy so you are advised to only update iasl-dev really.