A useful server welcome program for ComputerCraft, complete with hackermans style tendrils in the background. Can be used to show server rules and other important messages.

ComputerCraft Matrix Program.lua

--[[ Configuration ]]--
-- Max amount of tendrils on screen at a time
max_tendrils = 50

-- How fast the screen updates
-- note: Setting it to 0 or less will cause program to not work properly
update_speed = 0.25

-- Possible colors tendrils can be
-- note: the more you put the same color in a table, the more likely it is to be chosen
cols = { colors.white, colors.gray, colors.lightGray, colors.white, colors.gray, colors.lightGray, colors.white, colors.gray, colors.lightGray, colors.white, colors.gray, colors.lightGray, colors.green }

-- Messages to be displayed, line by line, in a box in the center of the screen
-- Set to {""} if you want a blank line
message = { 
	{"SERVER RULES", colors.pink, 1}, 
	{"==============", colors.red, 1}, 
	{"1. No stealing or griefing", colors.green}, 
	{"2. Do NOT use mods that create lag", colors.cyan},
	{"   without admin approval", colors.cyan}, 
	{""}, 
	{"SPAWN AREA", colors.yellow, 1}, 
	{"============", colors.orange, 1}, 
	{"If you want a portal in the spawn room,", colors.magenta, 1},
	{"ask an admin to set you up!", colors.magenta, 1}
}
-- Message format: { <Message> [, Color, Position] } (where 0 = left aligned text, 1 = center aligned text)
--		default color = white, default position = left

-- Customizing the box - change these if you want different symbols
corner_symbol = "+"
horizontal_symbol = "-"
vertical_symbol = "|"
outline_color = colors.blue

-- dont touch below this line unless you know what you're doing :)
--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--
--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--

-- Get CC terminal info
w, h = term.getSize()

-- Get useful info about message
longest_line = nil
if message ~= nil then
	longest_line = string.len(message[1][1])
	for i = 2, #message do
		if message[i] ~= nil then
			local msg_len = string.len(message[i][1])
			if msg_len > longest_line then
				longest_line = msg_len
			end
		end
	end
end

-- "Tendril" = the line of hackermanz bits falling down the screen
tendrils = {}
tendril = { id = '', x = 0, y = 0, color = 0, length = 0 }

-- Generate a "random" UUID4
function uuid4()
	local template = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'
	return string.gsub(template, '[xy]', function(c)
		local v = (c == 'x') and math.random(0, 0xf) or math.random(8, 0xb)
		return string.format('%x', v)
	end)
end

-- Generate a single random letter, symbol, or number
function hacker_bit()
	return string.char(math.random(32, 126))
end

-- Creates a new tendril, assign its starting position along the top of monitor,
-- set its color, and generate an ID to have it removed
function tendril:new()
	o = { 
		id = uuid4(),
		x = math.random(1, w), 
		y = 1, length = math.random(math.floor(h / 6), math.ceil(h / 2.5)), 
		color = cols[math.random(1, #cols)]
	}
	
	setmetatable(o, self)
	self.__index = self
	return o
end

-- Remove tendril
function tendril:destroy()
	for i = 1, #tendrils do
		if tendrils[i].id == self.id then
			table.remove(tendrils, i)
			break
		end
	end
end

-- Update tendril position + tail
function tendril:update()
	term.setCursorPos(self.x, self.y)
	term.setTextColor(self.color)
	term.write(hacker_bit())
	
	for i = 1, self.length do
		term.setCursorPos(self.x, self.y - i)
		term.write(hacker_bit())
	end
	
	self.y = self.y + 1
	if self.y - self.length > h then
		self:destroy()
	end
end

-- Main program
while true do
	-- Clear terminal and reset cursor position
	term.clear()
	term.setCursorPos(1, 1)
	
	-- Create tendrils
	if #tendrils < max_tendrils then
		table.insert(tendrils, tendril:new(math.random(1, w)))
	end
	
	-- Update & draw tendrils
	for i = 1, #tendrils do
		if tendrils[i] then
			tendrils[i]:update()
		end
	end
	
	-- Draw message frame
	local start_x = (w / 2) - math.floor(longest_line / 2) - 2
	local start_y = (h / 2) - math.floor(#message / 2) - 2
	term.setCursorPos(start_x, start_y)
	term.setTextColor(outline_color)
	term.write(corner_symbol .. string.rep(horizontal_symbol, longest_line + 4) .. corner_symbol)
	for i = 1, #message + 2 do
		term.setCursorPos(start_x, start_y + i)
		term.write(vertical_symbol .. string.rep(' ', longest_line + 4) .. vertical_symbol)
	end
	term.setCursorPos(start_x, start_y + #message + 3)
	term.write(corner_symbol .. string.rep(horizontal_symbol, longest_line + 4) .. corner_symbol)
	
	-- Draw message
	start_y = (h / 2) - math.floor(#message / 2)
	term.setCursorPos((w / 2) - math.floor(longest_line / 2) + 1, start_y)
	for i = 1, #message do
		local x_pos = 0
		local y_pos = start_y + (i - 1)
		
		if message[i] ~= nil then
			if (message[i][3] == nil or message[i][3] == 0) then
				x_pos = start_x + 2
			else
				x_pos = (w / 2) - (message[i][1]:len() / 2) + 2
			end
		
			term.setTextColor(message[i][2] or colors.white)
		end

		term.setCursorPos(x_pos, y_pos)
		if message[i] then
			term.write(message[i][1])
		end
	end
	
	sleep(update_speed)
end