FLTK (pronounced "fulltick") is a cross-platform C++ GUI toolkit for UNIX/Linux (X11), Microsoft Windows, and Mac OS X. It provides modern GUI functionality without the bloat, and supports 3D graphics via OpenGL and its built-in GLUT emulation. FLTK is designed to be small and modular enough to be statically linked, and also works fine as a shared library. It also includes an excellent UI builder called FLUID that can be used to create applications in minutes.
The Free Library System (FLS) is a system for maintaining a database of items and borrowers of a library. The goal is to provide simple yet powerful and flexible ways to search for items, provide circulation functions, and communicate with other libraries running FLS. It is implemented in Java and uses JDBC to access a suitable database.
Flounder is a program to quickly visualize 4D data (x,y,z,t). It can produce isosurfaces, solid renderings, as well as 2D slices. Several data sets can be viewed simultaneously. Temporal data at a spatial location can be examined with output in several formats including PNG and GIF animations.
floppyfw is a router and simple firewall on one single floppy. It uses Linux basic firewall capabilities, and has a very simple packaging system. It is perfect for masquerading and securing networks on ADSL and cable lines, using both static IP, DHCP, and PPPoE, and provides a simple installation, which usually involves editing of only one file on the floppy.
fli4l is a single-floppy Linux-based ISDN/DSL/ethernet-router. It features configuration with some simple ASCII-files, several possible connection-flavors (in/out/callback, and raw IP/PPP), channel bundling (an extra channel can be added through a Windows/Unix-client), configuration of multiple networks, least-cost routing, automatic choice of provider, display/calculation of connection times and costs, and a Windows/Unix client to control dial/hangup, monitor traffic and monitor incoming calls on ISDN (see screenshot).