If you are looking for an open source alternative to Roam Research, TiddlyWiki is your best bet. Because it’s self-hosted—meaning you keep your data private—it may seem a bit more daunting to get started. So here is a guide which will take you from complete beginner to completely in love …
Using TiddlyWiki as an alternative to Roam.
Getting started with TiddlyWiki: a beginner’s tutorial – Ness Labs
