Basic circuits such as 16-bit ripple carry adder, full adder, half adder, and mux. You can use GHDL to compile testbenches and check it. For example, Add16.vhd describes the circut, Add16_tb.vhd describes the testbench.

Run You need GHDL to run testbenches on computer If you have GHDL, you can type

"make halfadder" "make fulladder" "make add16" "make mux"

You can check vcd output at work directory to see signals.