If you appreciate Icarus Verilog and would like to make a donation, you can do so. Donations do not directly buy you anything, not special attention or support, not even a T-shirt; but they do deliver flexibility, and maybe a pizza, to the authors, who will endeavor to apply the funds in support of open software development. Donations are not tax deductible, but they are very much appreciated.
The donation payment is done through PayPal. They will accept credit card and PayPal transfers. This button takes you there. Seriously, your support is helpful and very much appreciated.
If you are interested in paying for specific work on Icarus Verilog, See the "Commercial Support" heading here, and contact a support provider directly.
If you are (or have been) using Icarus Verilog long term and wish to donate on a regular schedule, you can subscribe. A subscription is exactly the same as a donation, but repeats every month. So if you subscribe for $5.00/month, your credit card will automatically be deducted $5.00 each month until you stop the subscription. Subscriptions are especially useful because they allow me to plan for infrastructure improvements that may involve repetitive costs. Even one-time costs (improved equipment, documentation, etc.) can be more readily planned for.