Site: https://ra4king.github.io/CircuitSim
Basic circuit simulator with many built-in components. Check out src/com/ra4king/circuitsim/simulator/components
for examples of how Components are written. Their GUI counterparts are in src/com/ra4king/circuitsim/gui/peers.
Screenshot
The gradle script produces a multi-release jar to resolve incompatibilities between JavaFX 8 and 9, so you need to install both Java 8 and Java 9 to build. For example:
$ export JAVA_8_HOME=/usr/lib/jvm/java-8-openjdk-amd64/
$ export JAVA_9_HOME=/usr/lib/jvm/java-9-openjdk-amd64/
$ ./gradlew jar