letX is a collaborative LaTeX editor that runs in your browser. Multiple people can write in the same project at once, with live cursors and edits that merge without overwriting — so teams don't have to email .tex files around or pay to collaborate. It compiles to PDF in about a second, no local install needed, with version history, SyncTeX syncing, and ZIP import for existing projects. We built it while writing our thesis, because real-time collaboration was paywalled on the tool we used. letX keeps unlimited collaborators free, includes 80+ templates, and never uses your writing to train AI. Used by students and researchers at 40+ universities.