Free Software for Linux
SpeedCrunch
SpeedCrunch is a free and open-source high-precision scientific calculator. The application features a fast, keyboard-driven user interface that displays results as you type. SpeedCrunch comes with over 80 built-in mathematical functions, if that's not enough, you can define your own functions. A library of built-in formulas that allows to you to review and insert commonly used formulas is also included. SpeedCrunch can be downloaded for macOS, Linux and Windows, and is licensed under the GNU General Public License.
Komodo Edit
Komodo Edit is a free and open source text editor designed for dynamic programming languages, inclduing PHP, Python, Ruby, JavaScript, Perl, Tcl, XML, HTML5, CSS and more. With Komodo Edit you can enjoy a development process supported by syntax coloring, folding, background syntax checking, and excellent auto-complete and code intellisense. Komodo Edit is developed and released as open source software by ActiveState, in an effort to provide an more accessible version of their commercial software Komodo IDE.
Joplin
Joplin is a free and open source note taking and to-do list application. Joplin can handle large number of notes organised into notebooks and allow you to write memorable notes using markdown. With Joplin your notes are searchable, can be copied, tagged and modified either from the applications directly or from your own text editor.
RethinkDB
RethinkDB is a scalable, open-source database designed for real-time applications. When your app polls your database for data, it becomes slow, unscalable, and cumbersome to maintain. RethinkDB solves this by providing a new database access model, where developers can instruct the database to continuously push updated query results to their applications, without polling.
Apache HBase
With Apache HBase manager realtime read/write access to your Big Data. Apache HBase is an open-source, distributed, versioned, non-relational database modeled after Google's Bigtable: A Distributed Storage System for Structured Data. Just as Bigtable leverages the distributed data storage provided by the Google File System, Apache HBase provides Bigtable-like capabilities on top of Hadoop and HDFS.
Yandex.Disk
Yandex.Disk is a free cloud service provided by Yandex. The software lets you store, backup and sync files in the cloud by dragging and dropping them into the browser window or via the mobile application. Yandex.Disk can be used for batch operations on files and folder, and allows the user to publish images to the web. The software is available for Android, iOS, macOS, Linux, Windows, Windows Phone and the web browser.
Todo.txt
With Todo.txt you can track your performance in a simple text file. Todo.txt provides a simple and intuetive text-based user interface that can be used in-application or in a command line tool of your choice. With a simple but powerful shell script called todo.sh, you can interact with todo.txt at the command line for quick and easy, Unix-y access.
Haroopad
Haroopad is a free and open-source markdown editor or document processor for creating web-friendly documents. The application gives you the same editing experience regardless of the platform you are working on. Haroopad is avalible for macOS, Linux and Windows.
BleachBit
BleachBit is a free and open-source disk space cleaner, privacy manager, and computer system optimizer that allow you to fully delete unanted files and improve privacy of your system. With BleachBit it's simple to clean cache, internet history, temporary files, logs, cookies, Firefox, Google Chrome, Flash, macOS, Linux, Windows and more. BleachBit is fully open-source and released under the GNU General Public License.
Perkeep
Perkeep is a set of free and open-source formats, protocols, and software for modeling, storing, searching, sharing and synchronizing data in the post-PC era. Data may be files or objects, tweets or 5TB videos, and you can access it via a phone, browser or FUSE filesystem. Perkeep is openly and actively developed and anyone is free the contribute to the project.