suncalc.org — Computation path of the sun
CyberChef — The Cyber Swiss Army Knife; a web app for encryption, encoding, compression and data analysis
Stirling-PDF — locally hosted web application that allows you to perform various operations on PDF files
sshx — Fast, collaborative live terminal sharing over the web
pgs.sh — A zero-dependency static site hosting service for hackers.
my90stv.com — Watch TV from the 90s and earlier
immich — Self-hosted photo and video backup solution directly from your mobile phone.
novel.sh — Notion-style WYSYWIG editor with AI-powered autocompletions
shapedivider.app, svgwave.in, getwaves.io, wavelry.vercel.app, haikei.app and codepen: Responsive && Configurable SVG Waves — multiple generators for wave-like svgs/images/backgrounds
Open-source maps for everyone, powered by Headway and OpenStreetMap
OpenRailwayMap (previously called "Bahnkarte") is a detailed online map of the world's railway infrastructure, built on OpenStreetMap data.
Advanced css gradient editor with multiple layer support
Numpad is a text editor/calculator hybrid.
From the HN comments, there is also calcpad ("A different take on the caculator"), an electron app where an online version is available too. Both nifty.
ansi-art — allows you to render a regular image as a 24-bit, Unicode-capable version of ANSI Art
free-for.dev — A list of SaaS, PaaS and IaaS offerings that have free tiers of interest to devops and infradev
15.ai — DeepThroat (/ˈdēpˌTHrōt/): Natural emotive high-fidelity text-to-speech synthesis