Running from source is quite simple, all you need is to have Java installed, or download GraalVM, a Java runtime that requires no installation.

Step 0: Building without installing Java

Download GraalVM and extract this to a folder. Set env variable JAVA_HOME to point to the extracted folder. For instance, run
export JAVA_HOME=/home/myuser/programs/graalvm-jdk-17.0.9+11.1
in the terminal before you start building Trunkfriends

Step 1: Obtaining the source.

Go to Version overview, find the version you want to download (probably the latest version), and press "downloads", and select to download source code either as ZIP or tar.gz archive. Extract the archive to a folder
You can also go to Main branch overview and press the blue "code" button, and select "download zip", or use git to clone the repos. If you select build from main branch, you get access to the very latest, unpublished features, but please note that you are more likely to run into bugs as extensive bug testing only happens prior to release.

Step 2: Running Trunkfriends.
Open a terminal / command window and navigate to the folder containing the extracted source package. Make sure you have Java in your path, version 17 or newer. type
java --version
to validate.
To run trunkfriends, write
sh gradlew run - on linux / unix / osx
gradlew.bat run - on windows