Before electronic tuners, guitarists tuned by ear against a reference note, and it is still one of the best ways to train your hearing. This page plays each string of your chosen tuning on a real guitar sound so you can match it on your own guitar, no microphone needed.
Tap a string to hear it. Choose Repeat this string and the note keeps coming back every few seconds while both hands stay on the guitar, or All strings in turn to cycle through the whole set. Strum open strings plays every string together, so you can hear what the tuning should sound like when it is right.
As you get close, listen for a slow wobble or beat between your string and the reference. The wobble gets slower as the two notes get closer and stops when they match. That wobble is the most precise tuning signal there is, and learning to hear it pays off for the rest of your playing life.
Every tuning from the alternate tunings tuner is here, along with bass tunings and any tuning you have saved. You can shift the reference an octave up or down, set a capo, change the time between notes, or change the reference pitch from A = 440 Hz.