The SIDKick pico ("SKpico") is a drop-in replacement for the SID 6581/8580 sound chips in the Commodore 64 and 128 computers. It has been designed as an inexpensive alternative to other replacements while not making compromises regarding quality. It consists of a simple interface board and a Raspberry Pi Pico (or compatible clone). The emulation is based on an extended version of reSID 0.16, and includes a few additional features.
Emulates the 6581 or the 8580 in single or dual SID mode. Has a built-in configuration menu that is accessed with a BASIC command (SYS 54301 for the c64, SYS 54333 for the c128). Supports stereo output if you hook a DAC up.
Uses surface mount components so this is not a project for the inexperienced or the faint of heart.
An FPGA powered hardware platform for emulating the MOS 6581 and 8580 SID chips. It is a fully functional device that can be installed into a Commodore computer as a pin-compatible replacement.
A fork of the last GNOME v2.x release, before GNOME 3 went and screwed everything up. It's being maintained and updated, and suggested as a usable replacement for the bloated, lovecraftian beast that GNOME 3 was out of the gate.
Classic Shell is an open source application for Windows 8 that gives you a sane and usable desktop by replacing the Start Menu. It's skinnable, too, so you can make it look like Windows 7, Windows XP, or other versions of Windows.
The SwinSID is a pin-compatible and software-compatible replacement for the Commodore SID chip based upon an Atmega microcontroller. You can drop this chip right into a socket on the motherboard of a damaged Commodore computer, or you can probably drop it into a hardware synth that uses SID chips and hit the ground running. The firmware image and schematics are available for download for free on the website, so you can roll as many of your own as you want.
The μg Project is a collection of free and open development APIs that are fully compatible with Google's GAPPS APIs but use different back end services. For example, rather than Google Maps there is a library which uses Open Streetmaps instead, but code written to use the Google Maps API won't know the difference.