OptLowpass

OptLowpass™ is a specialized program written to expedite the design of transmitter output lowpass filters, especially for the HF amateur radio bands.
On startup, the program presents pre-designed lowpass filters for each of the HF amateur bands, using ideal parts values as outlined in the above-mentioned article.

You may also recall the last design session, recall a previously-saved design or invoke the Design Wizard.
The design page shows the schematic of the filter as designed and a plot of the responses of that filter (both transmission and reflection).