Originally, Qucs was composed of a circuit simulator "qucs-core", now Qucsator, and a GUI for schematic entry and plotting.

Later, support for other simulators has been added to cover VHDL, Verilog and SPICE engines to some extent.

The current roadmap aims to decouple schematic representation, device modelling and preferred simulator choices by means of adopting concepts from the IEEE1364 industry standard.

Other features include the transmission line calculator, Filter synthesis, Smith-Chart tool for power and noise matching, Attenuator design synthesis, Device model and subcircuit library manager, Optimizer for analog designs, the Verilog-A interface, Support for multiple languages (GUI and internal help system), Subcircuit (including parameters) hierarchy, Powerful data post-processing possible using equations and symbolically defined nonlinear and linear devices.

A component library manager gives access to models for real life devices (e.g. transistors, diodes, bridges, opamps).

The command line conversion program tool is used by the GUI to import and export datasets, netlists and schematics from and to other CAD/EDA software.

Some have been tested, these include Qucs-S is a fork of Qucs that supports the SPICE-compatible simulator backends of Ngspice, Xyce, SpiceOpus, in addition to Qucsator.