There are a couple of interesting child pages, so don't forget to check them out, via the site menu.
CyberChef - this is a fantastic toolbox to keep handy and does amazing things. You simply drag an Operation into the Recipe and type some Input, then you will see Output. There is an example at From Base64 - CyberChef which might help
Free Printable Graph Paper - includes a virtual version as well
Noisli - Improve Focus and Boost Productivity with Background Noise - does what it says and very well too
Hipstersound | Ambient noise generator to create a positive work environment - an alternative
This is software I am aware of and that should be good but I have not used:
SamKnows - Broadband Availability Checker
Time zone conversion - timeanddate.com
Convert to/from milliseconds - Current Millis ‐ Milliseconds since Unix Epoch
Sitespeed.io - Welcome to the wonderful world of Web Performance
WebPagetest - Website Performance and Optimization Test
Security Tools Top 10 (2013) - ToolsWatch.org – The Hackers Arsenal Tools » 2013 Top Security Tools as Voted by ToolsWatch.org Readers
MD5 File - HTML5 File Hash Online Calculator - MD5, SHA1, SHA2 (SHA-256), SHA-384, SHA-512
Security Planner - gives some good security advice
SSL Labs - Qualys SSL Labs - Projects / SSL Server Test
Symantec - SSL Toolbox
Hardeniuze, site testing - Hardenize: Comprehensive web site configuration test
This is a file transfer format, however OpenAS2 Server Application is a useful open source product.
Linux based partition utility - GParted -- A free application for graphically managing disk device partitions, not use myself
Commercial disk/partition utility - Disk Management Software - Acronis Disk Director 12 which I heartily recommend
<input> - HTML | MDN - be sure to use the correct or best type
HTML Standard - the definitive spec on HTML 5
HTML5test - How well does your browser support HTML5? - test your browser
Relax-and-Recover - Linux Disaster Recovery - stumbled upon this, never used but looks interesting
Network West Midlands - Tram or National Express Midland Metro - Birmingham Trams
Stagecoach Supertram: home - Sheffield Trams
Every Journey Matters - Transport for London - TfL
Raildar - Historic train arrival times
OpenTrainTimes
How to start with Qt? | nidomiro - a good introduction
C++ Qt Programming - YouTube - some introduction videos
Alexa Top 500 Global Sites - most popular websites
Have I been pwned? Check if your email has been compromised in a data breach - "haveibeenpwned" is run by Troy Hunt, security researcher, so can be trusted
General Data Protection Regulation (GDPR) – Final text neatly arranged - for the full GDPR documentation
Tower Bridge | London’s Famous Bridges | London Landmarks
Stay safe in London | The Met
Theft tactics: Be Aware of thieves' tactics | British Transport Police
Rail Map online - historical rail maps
Godot Engine - Free and open source 2D and 3D game engine
Home | mRemoteNG - colleagues have used this, looks worth trying
Remote Desktop Manager - Remote connection and password management software - installed on client's machines, commercial product, possibly worth a look
Picture Sheffield - Images of Sheffield from the council archive
Northern Powergrid | Power Cuts - check if you have an electrical power cut in Sheffield, Yorkshire or the North East
BMI healthy weight calculator - Health tools - NHS Choices
Julian Treasure: How to speak so that people want to listen | TED Talk
Quod Libet is written in Python and uses a Python library for manipulating audio file metadata, specifically the tags, see Overview — mutagen for details.
Discord - Free Voice and Text Chat for Gamers - for gamers to replace Skype or TeamSpeak but can be used generally
Video Meetings, Video Conferencing, and Screen Sharing - Whereby (formally appear.in) - meeting focused, supports screen sharing, either with a Chrome extension, or it just works in Firefox
Zoom - supports conferences
Firefox Send - for file sharing
Jitsi Meet - secure and free video conferencing
The following sites might be useful for solutions you are building:
Specifically COVID-19