Select several files and get one back, in the order you chose them. Mismatched sample rates and channel counts are sorted out for you, and nothing is uploaded.
What it does
Joining audio sounds trivial and mostly is, until the files disagree with each other. One is 48kHz because it came out of a video editor, another is 44.1kHz because it came off a CD rip, a third is mono because it was recorded on a phone. Append those naively and one section plays at the wrong speed while another comes out of a single speaker.
This resamples everything to the highest rate present and places mono material across both channels before joining, so the result is consistent from end to end. The files are combined in the order you selected them, and the whole operation happens in your browser — no upload, no queue, no account.
There is also a crossfade control. Set it to zero for a hard cut between sections, which is what you want when the material is already edited; give it a second or two when you are running tracks together and would rather not hear the seam.

How it works
Select, set the crossfade, download.
Multi-select in the file picker. They are joined in the order you pick them, so select them in the order you want to hear them.
Leave the crossfade at zero to butt them together exactly, or dial in a second or two to blend each transition.
Play it through first, then take it as a WAV or an MP3.
What you get
This is where naive joiners fall over. Everything is brought to a common rate before the files are combined, so no section ends up playing fast or slow.
Each junction can overlap by as much as five seconds, with matched fade curves so the level stays even through the transition instead of dipping in the middle.
You do not need to convert the inputs to the same format first. MP3, WAV, FLAC, M4A, OGG and video files can all go into the same merge.
Every other online joiner sends your files to a server and sends one back. This runs in the page, which means no waiting on a queue and no copies of your recordings sitting anywhere.
Who uses it
Run tracks together with a crossfade for a party, a workout or a set you want to play unattended.
Intro, the recorded conversation, the ad read, the outro — four files, one export.
Stitch a recording that was captured in sessions back into a single file for the drive.
Cut sections out of several songs, then join them into one track in the order the routine needs.
Recorders often break a long take into fixed-size files. Joining them puts the take back together.
Line up a series of takes end to end so you can listen through them in one pass.
FAQ

Select your files, set the crossfade, download a single track.