GKrellM is a single process stack of system monitors which supports applying themes to match its appearance to your window manager, Gtk, or any other theme.
GKrellM vs Conky opinions
Cross platform, Open source and Configurable in a user-friendly way, Definitely the best alternative in my book
Works flawlessly out of the box, while being nice to look at as well.
I've used GKrellM for years in Linux. Very simple to set up and displays the info I like to keep an eye on. I didn't realise it's available on Windows too.
vtop is a graphical command-line tool that uses unicode braille to chart CPU and memory usage. It can be easily extended.
Elkowars Wacky Widgets is a standalone widget system made in Rust that allows you to implement your own, custom widgets in any window manager.
GonhaNG is a light-weight system monitor for Linux, its display weather forecasts, date, time, cpu temperature, memory load, cpu load, filesystems and network stats (download and upload rate).
MagicMirror² is an open source modular smart mirror platform. Based on the Electron application wrapper and tested (but not limited to) Raspberry Pi single board computers.
BGINFO for X, also called BGINFO4X, is a clone of the popular program BGINFO for Windows created by Sysinternals.This app doesn't have any features at the moment.Discontinued
last post or update 2014
gDesklets is an architecture for "desklets", which are tiny applets sitting on your desktop in a symbiotic relationship of eye candy and usefulness.Discontinued
The project is no longer developed and the official website is no longer available. Last version, 0.36.3, released in January 2011, can be still downloaded from Launchpad
This program is a GTK3-based wrapper to display a script output, or a text file content on the desktop in sway or other wlroots-based compositors. It uses the gtk-layer-shell library to place the window on the bottom layer.