Are you looking to do analog or digital designs? We develop a number of tools ourselves, but most of the simulation tools are open-source and developed by others, such as ngspice or Xyce for analog simulation, or iverilog or verilator for digital simulation. Since you mention schematics, I'll assume you want an analog design flow. For that, you can use xschem for schematic entry and schematic capture, and you can use klayout or magic for layout.
The best channels here for learning about the analog flow tools are #analog-design, #xschem, #xyce, #klayout, and #magic .