Tenon.io does intend to continue to have a free account level; it may have limited options (such as a limit on the number of queries per month, for example), but there will be a free version.

Additionally, Karl has said he's committed to providing free API access for open source projects - so if you're testing WordPress itself or using Tenon to test an open source project you're developing, the API access will be free.

The WAVE tool is also a very nice tool; it's just harder to collate the results, and will bring up a lot more false positives.

The strength of Tenon is in the ability to identify all the completely machine-testable issues on a site, so you can eliminate that noise from manual testing, like that done with the WAVE tool.

Thanks for sharing, Sarah!