TonedEar is a fantastic website for honing your aural musical skills. As a musician, your aural skills are those that rely solely on your ears and intuition. This website features a variety of exercises that test different aspects of your aural musicianship including identifying scales, chords, intervals, and chord progressions. Each exercise is fully customizable; You can edit exactly what appears in each question, how many questions you answer, whether you hear the notes ascending, descending, or at the same time, AND how fast you hear the notes change. The link above will take you to the “intervals” exercise, which serves as the foundational aural skill for all of music. Once you can easily identify intervals, everything else will be a breeze. 

Musictheory.net is a great tool for sharpening your theory knowledge. Theory is the next thing you should be pretty familiar with as a musician. This website provides you with numerous exercises that cover most aspects of music theory including both the identification and construction of notes, intervals, chords, scales, and key signatures. These exercises don't just pertain to the notes on the staff either, you can also perform the same exercises but with the keys on the piano keyboard. The website also provides helpful tools for completing theory homework or lessons; These include accidental, interval, and key signatures calculators, a roman numeral analysis generator, a matrix generator, a pop-up piano, and digital staff paper. The link above will take you to the chord builder exercise where you are tasked with raising, lowering, or ignoring certain notes in the triad to create the listed chord quality. 

4four is an online tool similar to tonedear, but rather than train your melodic and harmonic aural skills, you are focusing on rhythm identification. This website has a bunch of fun games you can play to help improve your ability to identify and read rhythms. These exercises include identifying the rhythms you hear per beat, per measure, identifying the incorrect beat pattern, tapping the rhythms you see, and even identifying which percussion instruments you hear in each example. The website also offers a variety of tools to help with rhythm which includes a metronome, a random rhythm generator, a rhythm looper, and a groove creation tool. Each exercise is also fully customizable; You can edit what kinds of rhythms you hear, how fast they are, the time signature, what instruments you hear, and how many questions appear. The exercise linked above is one in which you will hear a full measure of rhythm and out of the multiple choices of beat units, you are supposed to recreate the rhythm.