"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, can be copied, tagged and modified either from the applications directly or from your own text editor. The notes are in Markdown format."
WorkFlowy is an organizational tool that makes life easier. It can help you organize personal to-dos, collaborate on large team projects, take notes, write research papers, keep a journal, plan a wedding, and much more.
Trello is a collaboration tool that organizes your projects into boards. In one glance, Trello tells you what's being worked on, who's working on what, and where something is in a process.
5pm (www.5pmweb.com) is a web-based project management tool. It has a smart customizable interface - everything within a click or two. 5pm packs a lot of features like Reports, interactive Timeline (Gantt), email integration and more.