I've been playing and organising a game of
5-a-side football with some mates on and off for about 10 years.
If you do the same, you have my sympathy as it's a right faff.
Around 6 or 7 years ago I wrote a simple Excel spreadsheet
that helped a little as I could store everyone who was interested in playing, generated all the e-mails, flag who was playing and who
wasn't, etc. It was better than a pen and paper, but I still had to remember to fire the spreadsheet up and send out invites, and
remember to send reminders (Outlook for that one).
A few years into changing jobs
and here we are with version 2 of the spreadsheet, toepoke.co.uk.