-
InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
I use Mnemosyne. It is free, it uses a scheduling algorithm that is similar to Anki, it supports HTML in the cards (with audio, video, kanji/kana, furigana, etc.), and it can import Anki decks.
NOTE:
The number of mentions on this list indicates mentions on common posts plus user suggested alternatives.
Hence, a higher number means a more popular project.