Foam is described as 'personal knowledge management and sharing system inspired by Roam Research, built on Visual Studio Code and GitHub' and is an app in the Office & Productivity category. There are more than 100 alternatives to Foam for a variety of platforms, including Online / Web-based, Windows, Mac, Android and Linux. The best alternative is Joplin, which is both free and Open Source. Other great apps like Foam are Standard Notes (Freemium, Open Source), Google Keep (Free), Notion (Freemium) and Microsoft OneNote (Freemium).
Notational Velocity is a mouseless application for storing and retrieving notes. With Notational Velocity, searching for notes is not a separate action; rather, it is the primary interface. Searching encompasses all notes content and occurs instantly with each key pressed.
NixNote, formerly Nevernote, is an open source client for Evernote . It is written in Java so it will also run on Windows & OS-X, but the primary focus has been to try and get a usable environment for Linux.