You can run Pyre without using watchman if your editor-of-choice supports LSP -- the two modes are basically complementary. You can also run `pyre check` in non-incremental mode, though that may be slower depending on the size of your codebase.
Edit: for the active file / LSP part, I mean it shows errors mainly for the active file.
Edit: pyre will show type errors for all files in your repository, not just the ones you have open.