Below taken from the subreddit. Link

Methodologies

Abbreviation: What it means:
FOSS Free and open-source software
Free Everything that is part of the app is free
Free +$ Free, but has additional paid features
Paid Most or all features are paid
+ n.desktop with native desktop app
nn. non-native
W/M/L Windows/Mac/Linux
iOS/A iOS/Android
BDL Bidirectional linking
Links Regular links between notes

Side note 1: Apps that have both web & native apps are under “Web-based applications” and are specified accordingly, however, only native apps are under “Native applications”.

Side note 2: Native apps assume local storage unless otherwise stated.

Side note 3: If there’s a question mark somewhere, it means that I’m not sure. If you know what correctly belongs there, I’d appreciate it if you let me know in the comments. Thanks.