WPILib provides the core libraries for creating robot programs with the roboRIO. WPILib uses Gradle to build and deploy code.
FRC Robots will transition to a new robot controller for the 2021 season, developed by REV Robotics. This may significantly change the way you interact with the controller.
CTRE provides various electrical components and software libraries for FRC (e.g. TalonSRX, Falcon 500, CANifier, Phoenix Tuner). Software downloads can be found under the technical resources section of their respective product page.
REV Robotics provides various electrical components and software libraries for FRC (e.g. SPARK MAX, NEOs, Through-bore Encoder). Note that REV Robotics provides documentation on a part by part basis, rather than centralizing their documentation.