kdb is mentioned. Possible it was added after your comment in the last 30 mins, but the article is about open source not proprietary.
EDIT: yeah that sentence is new. I think some of the sentences around Influx being the "first" have been adjusted too now saying it is the first "mainstream" and called other db's niche. it's also a little off. KDB+ is more popular in large banks and trading firms than HFT places.