UnityOS

os.pullEvent = os.pullEventRaw
local w,h = term.getSize()
function printCentered (y,s)
    local x = math.floor((w - string.len(s)) /2)
    term.setCursorPos(x,y)
    term.clearLine()
    term.write(s)
end

--Draw menu Function
local nOption = 1
local function drawMenu()
    term.clear()
    term.setCursorPos(1,1)
    term.write("UnityOS")
    term.setCursorPos(w-11,1)
    if nOption == 1 then
        term.write("Command  ")
    elseif nOption == 2 then
        term.write("Programs ")
    elseif nOption == 3 then
        term.write("Restart ")
    elseif nOption == 4 then
        term.write("Shutdown ")
    elseif nOption == 5 then
        term.write("Uninstall")
    else
    end
end

--GUI
term.clear()

local function drawFrontend()
    printCentered(math.floor(h/2) - 3, "")
    printCentered(math.floor(h/2) - 2, " Menu ")
    printCentered(math.floor(h/2) - 1, "")
    printCentered(math.floor(h/2) + 0, ((nOption == 1) and "[ Commands  ]") or "Commands ")
    printCentered(math.floor(h/2) + 1, ((nOption == 2) and "[ Programs  ]") or "Programs ")
    printCentered(math.floor(h/2) + 2, ((nOption == 3) and "[ Restart   ]") or "Restart  ")
    printCentered(math.floor(h/2) + 3, ((nOption == 4) and "[ Shutdown  ]") or "Shutdown ")
    printCentered(math.floor(h/2) + 4, ((nOption == 5) and "[ Uninstall ]") or "Uninstall")
    printCentered(math.floor(h/2) + 5, "")
end

--Display

drawMenu()
drawFrontend()

while true do
    local e,n = os.pullEvent("key")
        if e == "key" then
            if n == 17 or n == 200 then
                if nOption > 1  then
                    nOption = nOption - 1
                    drawMenu()
                    drawFrontend()
                end
            elseif n == 31 or n == 208 then
                if nOption < 5 then
                    nOption = nOption + 1
                    drawMenu()
                    drawFrontend()
                end
            elseif n == 28 then
                break
            end
        end
end

term.clear()

--Conditions
if nOption == 1 then
    shell.run("OS/ .command")
elseif nOption == 2 then
    shell.run("OS/.programs")
elseif nOption == 3 then
    os.reboot()
elseif nOption == 4 then
    os.shutdown()
else
    shell.run("OS/ .uninstall")
end