ah! sorry, i was actually hoping you would say something like “lemurs? but there is no option! here is how i did it in my config:”, and then i would have yoinked it. but if i HAD to guess with my limited knowledge of nixOS, it would be a shell script that just simply launches the binary, after all, its just a CLI command, right?
first, obvs, install pkgs.lemurs lol, and then lets try launching it on logind, i assume?:
environment.extraInit = ''
${pkgs.lemurs}/bin/lemurs # or just 'lemurs'?
'';
or
environment.etc."xdg/autostart/lemurs.desktop".text = ''
[Desktop Entry]
Type=Application
Name=lemurs
Exec=sh -c "lemurs"
NoDisplay=true # or 'false'? idk
'';
or even
systemd.services.lemurs = {
enable = true;
serviceConfig = {
ExecStart = "lemurs"; # or "${pkgs.lemurs}/bin/lemurs"?
# Type = "exec"; # or "simple"?
};
# script = "lemurs"; # instead of ExecStart?
};
UPDATE: i just tested these. NOPE, it tries to launch but lemurs fails with:
Failed to open log file: '/var/log/lemurs.log'
so, someone has to make a lemurs service option…
…
i dont know!!! these are my guesses, I HAVE NOT TESTED THESE, sorry, and i also dont have the time right now… please someone correct me or tell me i did it right 
oh, and i completely forgot: here is my tuigreet setup that, if i got that right, you were not able to configure:
silly colours example whatever with everything enabled (for small screen sizes! PDAs, steam deck & MNT pocket) (you will probably need console.font = "latarcyrheb-sun32" for a larger TTY font and better readability. idk how to pronounce that
services.greetd = {
enable = true; # "programs.uwsm.enable"?
package = pkgs.greetd.tuigreet;
restart = true; # optional
# vt = 1; # tty
settings = {
default_session = {
command = "${pkgs.greetd.tuigreet}/bin/tuigreet -w 69 -t --time-format '%B, %A %d @ %H:%M:%S' -r --remember-session --asterisks --user-menu -g 'Password: ********' --container-padding 1 --prompt-padding 0 --theme 'border=magenta;text=white;prompt=cyan;time=green;action=yellow;button=red;container=black;input=white'";
user = "greeter"; # NOT a username
# ...
};
};
};
to remove systemd spam in TTY login managers, use the thing above which edits the service’s StandardOutput
my ly config is WIP, im figuring out whether the colours are hex ARGB ro hex RGBA…
edit: okay got it. it’s 24-bit 0xSSRRGGBB, where SS is styling, as defined here:
#define TB_BOLD 0x01000000
#define TB_UNDERLINE 0x02000000
#define TB_REVERSE 0x04000000
#define TB_ITALIC 0x08000000
#define TB_BLINK 0x10000000
#define TB_HI_BLACK 0x20000000
#define TB_BRIGHT 0x40000000
#define TB_DIM 0x80000000
okay, got a config going. this one’s psychedelic 
services.displayManager.ly = {
enable = true;
package = pkgs.ly; # TUI -- zig -- https://codeberg.org/AnErrupTion/ly
x11Support = true;
settings = {
# allow_empty_password = false; # dangerous?
animation = "colormix"; # "doom", "matrix", "colormix"
animation_timeout_sec = 300; # 5 minutes
auth_fails = 3; # special animation looks broken?
bg = "0x02000000";
# bigclock = "en"; # enlarges the clock -- may not work with some fonts?
# blank_box = false; # transparent
border_fg = "0x01FFFFFF";
box_title = "null"; # text above the box
clear_password = true;
clock = "%B, %A %d @ %H:%M:%S";
colormix_col1 = "0x08FF0000";
colormix_col2 = "0x0800FF00";
colormix_col3 = "0x080000FF";
default_input = "password";
error_bg = "0x02000000";
error_fg = "0x01FF0000";
fg = "0x01FFFFFF";
hide_borders = true;
hide_version_string = true; # doesnt work?
hide_key_hints = true;
initial_info_text = "null"; # hostname
# input_len = 69;
lang = "en";
load = true;
margin_box_h = 0;
margin_box_v = 0;
min_refresh_delta = 100; # milliseconds -- default=5
# numlock = true;
save = true;
text_in_center = false; # ugly
# tty = 4; # broken? -- could help with UWSM sessions
# vi_default_mode = "insert";
# vi_mode = true;
# ...
};
};
i wouldve provided a screenshot but idk how to screenshot a tty, yknow…
anyway, i have lots of things to share, but the nixOS community is not ready for my 10k lines config yet… 
update: you dont have to use pkgs.greetd.greetd to download the whole thing, you can just use pkgs.greetd.tuigreet
. Furthermore, it seemed to ignore the default settings as defined in nixpkgs and would instead try to use the defaults from the source (for example the shutdown command would complain that some path was missing - the path in question was defined in the source code, it was not the path from the nixpgk)