This page has some useful things-a metronome and a tuner. Playing with a metronome, or singing with a metronome is really helpful to establish a solid sense of time and rhythm and it’s a great habit to get into.
If you are starting out on guitar, try to use your ears with the ear tuner and make sure you recognise what order the strings come in.

Metronome by

Two tuners here. One works by ear-you listen to the notes and adjust your guitar accordingly. This is great for developing your ear. You can also use one which picks up the guitar sound from the computer microphone, although I’d advise you to trust your ears.