Bubbles!

local bubbles = {}
local bubbleChars = { "0", "O", "o", ",", "*" }
local x, y = term.getSize()
term.setBackgroundColor( colors.blue )
term.setTextColor( colors.lightBlue )
term.clear()

local rise = {
	["0"] = 3,
	O = 3,
	o = 2,
	[","] = 1,
	["*"] = 1,
	["."] = 1,
}

for i = 1, x, 3 do
	bubbles[ #bubbles + 1 ] = { c = bubbleChars[ math.random( 1, #bubbleChars ) ], x = i + math.random( 0, 2 ), y = y - math.random( 0, 3 ), ly = 1}
end

local id

while true do
	id = os.startTimer( 0.05 )
	for _, bubble in ipairs( bubbles ) do
		if bubble.y < 1 then
			bubble.y = y
			bubble.c = bubbleChars[ math.random( 1, #bubbleChars ) ]
			bubble.lx = bubble.x
			bubble.x = bubble.x + math.random( -1, 1 )
		end
		term.setCursorPos( bubble.lx or bubble.x, bubble.ly )
		term.write( ' ' )
		term.setCursorPos( bubble.x, bubble.y )
		term.write( bubble.c )
		bubble.ly = bubble.y
		local doesRise = math.random( 0, rise[ bubble.c ] ) > 0
		bubble.y = bubble.y - (doesRise and 1 or 0)
		bubble.lx = nil
	end
	while true do
		local event, tid = os.pullEvent( "timer" )
		if id == tid then
			break
		end
	end
end