An update from SimplyTest maintainers AmyJune and Adam:

In late 2019, simplytest.me joined OpenCollective (https://opencollective.com/simplytestme), allowing transparency around accepting donations and creating expenses. The Open Collective Foundation (https://opencollective.com/) is a 501(c)(3) organization collecting these contributions on our behalf. Because of this, contributions to simplytest.me through OpenCollective are tax-deductible for US taxpayers.