Here is a list of all known Gemini-related software. If you've written some Gemini software which is not listed here, please contact me at solderpunk@posteo.net.
Agate, a Gemini server written in Rust
Blizanci, a Gemini server writen in Erlang
GeGoBi, a Gemini server for Gemini-Gopher bi-hosting
Geminid, a Gemini server written in C
Gemserve, a Gemini server written in Rust
Germinal, a Gemini server written in Common Lisp
GLV-1.12556, a Gemini server (in fact, the first!) written in Lua
Jetforce, a Gemini server written in Python
The Unsinkable Molly Brown, a Gemini server written in Go
Net-Gemini, a Gemini server written in Go
Pollux, a Gemini server written in Rust
A bare-bones but usable Gemini client in 100 lines of Python
A bare-bones but usable Gemini client in 100 lines of Lua
A bare-bones but usable Gemini client almost 100 lines of Go
A Gemini client library in Guile Scheme
A more recent fork of the above library
A rich Gemini client library in Nim
Amfora, a very feature-rich Germini client for the terminal
Asuka, a ncurses-based Gemini client
AV-98, an experimental Gemini client derived from VF-1
Bombadillo, a multi-protocol client handling Gemini since 2.0.0
Castor, A graphical Gemini client written in Rust
Diohsc, a terminal Gemini client written in Haskell
elpher, a emacs-based Gopher and Gemini client
gacme, a Gemini client for plan9's Acme
gcat, a `cat`-like Gemini client
Gemget, a command-line Gemini downloader ala wget
GemiNaut, a user-friendly GUI client for MS Windows
gurl, a `curl`-like Gemini client
Gusmobile, a Gemini client library in Python
Kristall, a graphical Gemini client using Qt
McRoss, a graphical Gemini client written in Python/Tkinter
Moonlander, a very fancy graphical Gemini client written in Rust
ncgopher, a Gopher and Gemini client written in Rust
Rhapsode, an "auditory web browser" which supports Gemini
Twin Peaks, a graphical Gemini client written in C#
Zain, a graphical Gemini client written in Tcl/Tk
dillo-gemini, a Gemini plugin for the Dillo browser
text/gemini syntax highlighting for emacs
text/gemini syntax highlighting for kakoune
text/gemini syntax highlighting for nano
text/gemini syntax highlighting for vim
Agena, a Gemini-to-Gopher proxy
Atomini, a Ruby script to generate an Atom feed from a Gemini map
CAPCOM, an Atom feed aggregator that outputs text/gemini
Gemfeed, a tool to generate Atom feeds for a directory of text/gemini files
Gemgit, a tool to generate static Gemini pages for git repos
Gig, a Gemini application framework in Go
git.gmi, a Gemini git frontend
md2gemini, a Markdown to text/gemini converter