Logseq - Logseq is a local-first, non-linear, outliner notebook for organizing and sharing your personal knowledge base.
PopMan - PopMan is a POP3 and IMAP4 manager.
Mail Notification - Mail Notification monitors your mailboxes for new mail.
GNOME Gmail - Gnome Gmail is software which adds support for Gmail to the Linux Gnome Desktop.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
Mimestream - A native macOS email client for Gmail