Thank you for considering a donation to help with Sigil’s development. We’re glad you find Sigil useful enough to want to contribute.
But neither of Sigil’s current developers are accepting donations at this time. This is a hobby for both of us, and we enjoy volunteering our time and talents to Sigil. We’re leaving this link functional in case future Sigil developers ever do wish to accept donations for their efforts (and to avoid 404 errors in older versions of Sigil 
).
In the meantime, if you truly wish to donate something, consider donating your time and Sigil knowledge by answering user questions in Sigil’s user support forums, and/or by contributing to Sigil’s User Guide.
Thank you for your interest.