TkGate is described as 'Event driven digital circuit simulator with a tcl/tk-based graphical editor. TkGate supports a wide range of primitive circuit elements as well as user-defined modules for hierarchical design' and is a circuit simulator in the education & reference category. There are nine alternatives to TkGate for a variety of platforms, including Windows, Linux, Web-based, Mac and Self-Hosted apps. The best TkGate alternative is Circuit JS, which is both free and Open Source. Other great apps like TkGate are Logisim, Hradla, Logisim Evolution and Digital Logic Sim.
Has many components, no installation needed (in browser).