IconVault's Tone Generator plays pure test tones using the Web Audio API, with sine, square, sawtooth and triangle waveforms on a logarithmic 20 Hz to 20 kHz slider, adjustable volume, and a frequency sweep mode where you set the start frequency, end frequency and sweep duration.

Everything is generated live in your browser, so there are no audio files to download and nothing to upload, and the tool is free with no signup. The honest note: exact pitch perception depends on your speakers or headphones, so cheap laptop speakers will not reproduce very low bass tones accurately.