ZenPen is a minimalist, distraction-free writing tool. It supports only a few formatting tools like bold, italics, quotes and links. You can also toggle full-screen, invert the colors (night-mode) and set a target word count. Once you are done, you can save your work in HTML or plain text.
ShareDrop is a HTML5 clone of Apple's AirDrop. It lets you transfer files between devices on the same local network. It uses WebRTC for secure peer-to-peer file transfer and Firebase for presence management and WebRTC signaling. The ShareDrop app itself is open-source, so you can actually host it yourself if you are so inclined.
Sharefest lets you share a file by dragging-and-dropping it into the browser and instantly obtaining a disposable URL for sharing. No sign-up is required. It works by using WebRTC to perform BitTorrent-like P2P file sharing, so the more popular the file, the faster the transfer. Users can help seed the file by simply keeping their browser tab open after the download is complete.