You must use Windows 10/11 x64 to build the project. Build in other versions of Windows is not guaranteed.
Download and install Visual Studio Community 2019.
2.1. Desktop development with C++ workload should be selected when installing.
2.2. SDK 10.0.18362.0 should be selected when installing.
2.3. ATL/MFC libraries should be selected when installing.
2.4. English language pack (required for vcpkg).
Download and install CMake (version >= 3.17.0).
Download and install vcpkg4aspia (forked from Microsoft repository).
In vcpkg, you need to install the following libraries (use triplet x86-windows-static in all cases):

asio
curl
gtest
libvpx
libyuv
mimalloc
openssl
opus
protobuf
qt5-base
qt5-translations
qt5-winextras
rapidjson
sqlite3
zstd

Go to the directory with source code (root directory) and run the following commands:
mkdir build cd build cmake ..\ -G "Visual Studio 16 2019" -A Win32 -DCMAKE_TOOLCHAIN_FILE=<vcpkg_path>\scripts\buildsystems\vcpkg.cmake -DVCPKG_TARGET_TRIPLET=x86-windows-static (replace <vcpkg_path> with real path to vcpkg)
You can also use CMake GUI for these purposes.
After these actions, the aspia.sln file will be generated in directory “build”.
Open aspia.sln in Visual Studio and build the project.

Linux

The build for Linux was tested only in Ubuntu 20.04 and Debian 11.0. If you have a different distribution kit or its version, then additional steps may be required.

Install the following packages in your package manager (packages must be installed before installing vcpkg and its packages):

ninja-build
autoconf
autoconf-archive
autopoint
python
bison
gperf
libgl1-mesa-dev
libglu1-mesa-dev
libharfbuzz-dev
libfontconfig1-dev
libfreetype6-dev
libx11-dev
libx11-xcb-dev
libxext-dev
libxfixes-dev
libxi-dev
libxrender-dev
libxcb1-dev
libxcb-glx0-dev
libxcb-keysyms1-dev
libxcb-image0-dev
libxcb-shm0-dev
libxcb-icccm4-dev
libxcb-sync0-dev
libxcb-xfixes0-dev
libxcb-shape0-dev
libxcb-randr0-dev
libxcb-render-util0-dev
libxcb-xinerama-dev
libxcb-util-dev
libxkbcommon-dev
libxkbcommon-x11-dev
libatspi2.0-dev
libprocps-dev
libxdamage-dev
libxrandr-dev
libpulse-dev
flite1-dev
libspeechd-dev
speech-dispatcher
nasm
gcc
g++
qtcreator

In vcpkg, you need to install the following libraries (use triplet x64-linux in all cases):

asio
curl
gtest
icu
libvpx
libyuv
mimalloc
openssl
opus
protobuf
qt5-base
qt5-translations
rapidjson
sqlite3
zstd

Open QtCreator -> Tools -> Options -> Kits -> Qt Versions. Click the Add button and specify the path to /installed/x64-linux/tools/qt5/bin/qmake.
Open QtCreator -> Tools -> Options -> Kits -> Kits. Click the Add button. Enter a display name for the profile, specify the compilers (gcc/g++), and the Qt profile you added earlier.
Open CMakeLists.txt from the Aspia root directory in QtCreator and configure the build using the previously added profile.

Alternative instructions (SW build system)

Download, unpack and add to PATH sw tool from https://github.com/SoftwareNetwork/binaries
Run sw build source in the project root (example).
Binaries will be available under .sw/out directory.
To generate VS solution, run sw generate source.