Audio & video
The tools where running in your browser matters most. A video is the largest file most people ever handle, and every online converter makes you upload it first — then caps the size, stamps a watermark on the result, or asks for an email before the download. These read the file on your own machine instead: no upload to wait through, no limit but your own memory, and nothing added to what comes out. The same goes for the microphone and camera checks: what they capture is played back to you and never leaves the page, which is not a promise a site you are about to speak into should be asked to take on trust.
7 tools and counting
Mic TestA microphone test that answers the real question — will they hear me?Screen RecorderRecord your screen in the browser — nothing is uploaded anywhereWebcam TestA webcam test that tells you what the other end will actually seeAudio TrimmerTrim audio online — cut a piece out of an MP3 or a recording, with nothing uploaded.MP4 to MP3MP4 to MP3 in your browser — the audio out of a video as a real MP3, with nothing uploaded.Transcribe VideoTurn a video or audio recording into text, without uploading it anywhereVideo to GIFConvert video to GIF — MP4 to GIF in your browser, with the frames you choose.