This is a layout manager for the River window manager. It's a drop-in replacement for rivertile, but with a few things added and configuration per tag/output.
After you install, you can simply replace all instances of rivertile with filtile in your config to keep everything the same (but switch to per-tag configuration). If you want more than that, you can read the manual doc under the doc/ folder.
You can run the install.sh to install filtile (manual doc installation neeeds change INSTALL_DOC to yes in the script and run the script with root permission).
chmod +x install.sh
./install.sh