As the article states, Snowflake Data [1] and Wavefront [2] have been using it. SkuVault [3] is another company.

https://www.snowflake.net/how-foundationdb-powers-snowflake-...

https://www.wavefront.com/wavefront-foundationdb-open-source...

https://abdullin.com/sku-vault/foundationdb-layers/

There are probably several other companies from the original releases that haven't posted anything publicly, but it'll be awhile before we get full deployments from the latest open-source versions.