PDFsam
PDFsam – free simple and open source cross platform software for splitting and merging PDF files
qpdfview
qpdfview – free and open source software for viewing PDF documents with tab support
Okular
Okular is a free and open source, multi-platform document viewer that supports a variety of formats
Evince
Evince is a free and open source program for viewing PDF documents, comic books, and others.
Makagiga
Makagiga is a free and open source multi-platform simple software for creating to-do lists, notes, and reading RSS feeds
Purple Task
Purple Task is a free and open source simple software for managing tasks
OpenTodoList
OpenTodoList is a free, simple, cross-platform, open source software for creating notes and task lists
Planner
Planner – free and open source software for tracking your tasks, projects, and goals for Linux
Akiee
Akiee is a free and open source cross-platform program for maintaining a task list with Markdown support
Kapow
Kapow – free and open source multi-platform software for time tracking