BiglyBT

Source for BiglyBT.

Getting the basics to compile from source is pretty straightforward:

Clone the repo into your favorite IDE
Mark core/src and uis/src as project roots (source modules)
To the uis module, add core/lib/*, uis/lib/log4j.jar and one of the swt.jars at /uis/lib/
To the core module, add core/lib/*
Make uis module depend on core. Core should not depend on uis

Intellij will do all these steps for you with its wizard, and the only change you need to make is to remove one of the swt.jar files it found.

Running is only few more steps:

Main class is com.biglybt.ui.Main in uis
Working Directory should be a new folder, since the app will write things to it. Put the aereg.dll or libOSXAccess.jnilib in there.

When a normal user is running the app, the working directory is where the jar, executable, and libraries (dll, so, jnilib) are.
If you want a separate config dir from the default one, use VM Option -Dazureus.config.path=<some config path>
Run it