On IndieTide, the most voted indie alternative to Opal is Be Serious. The full list on this page is ranked by community votes and grows as new products launch.
How are these Opal alternatives ranked?
By community votes, most voted first. Makers list their own product as an alternative to Opal when they launch it on IndieTide, and signed-in members vote once per product.
How can I list my product as an Opal alternative?
Launch it on IndieTide and enter "Opal" in the "An alternative to" field of the submit form. Your product appears on this page once its launch week begins.