The Print Shop for the Apple ][, running in your browser. Download what you make as a PDF.
A collection of free homebrew games for a number of (emulated) systems, packaged for easily running on a Retropie.
fdpp: FreeDOS plus-plus.
The website for a classic space trading/warfare game called Elite run by one of the original authors. Includes a lot of information and even the novella which was published with the original version.
A wiki dedicated to the Commodore-64 home computer.
This is a copy of The Old School Emulation Center (tosecdev.org) maintained by Jason Scott at archive.org. It contains software, firmware images, documentation, texts, and much more for nearly 200 computer systems, from the Sinclair ZX Spectrum to the NCR Decision Mate V to the Kaypro II. If you're a retrocomputing enthusiast (or you're tasked with resurrecting a legacy machine for some reason) you'll want to poke around in here, you might find something helpful.
Software for composing music on a Linux box. Seems to have a tracker like interface. MIDI enabled. Seems to have a synthesis feature in addition to using samples. Can consolidate sequences into single objects. Embedded emulation of some of the greats, from the 303 and 803 to the 6581.