Open Source Software for Windows
wikidPad
wikidPad is a Wiki-like note taking application for storing your thoughts, ideas, todo lists, contacts, or anything else you can think of to write down. What makes wikidPad different from other notepad applications is the ease with which you can cross-link your information. Links in a wiki are created by typing in WikiWords. wikidPad allows you to get a better undestanding of your research and documentation and allow you to better explore and rediscover your knowledge.
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.
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.
Opera GX
Opera GX is a free gaming-centric web browser developed by Opera Software AS. The browser provides native integration to Discord and other chat applications and day and night mode built right into the browser itself. Opera GX was first announced at E3 2019 and is still in early access.
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.
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.
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.
KDevelop
KDevelop is a fully featured, plugin extensible IDE for C/C++ and many other programming languages. Supported platforms include Linux, Solaris, FreeBSD, macOS and other Unix flavors as well as Microsoft Windows. It is based on KDevelop Platform, the KDE Frameworks and the Qt libraries. KDevelop is a free and open source software under development by KDE since 1998.
Nextcloud
With Nextcloud, users can host their own secure cloud solution for file storage, collaboration and communication for enterprise or personal purposes. Nextcloud gives you full control over your own data and where and how you host it. The software can be hosted on-premise or on any VPS or cloud instance provided by third-party web hosts. If you value privacy and security, Nextcloud might be the right choice for you. Nextcloud is both free and open source and developed in an open, transparent and trustworthy manner.
nomacs
nomacs is a free, open source, cross-platform image viewer. With nomacs you can easily view and manage all common file formats including jpg, png, tif, bmp, raw and many more. The sleek user interface provided by nomacs features a semi-transparent widgets that display additional information such as thumbnails, metadata or histogram.