Back when ranked 5s was a separate queue, me and some friends playing them pretty seriously for about half a season before Riot got rid of it. Here's some things we used.
Calendar sync for us to plan practices
A bit obvious, but we had a bunch of notes in here: rules/policies, tryout process, general notes on what style we succeed with most, preferred champs, a table creating team comps using aforementioned champs.
Back then replay.gg was a big thing. I'd post the links to our games from the previous day, in a separate doc we would post our personal reviews of the VODs. I wanted us to review them together but it never really happened.
I thought I had some more suggestions, but a bunch of the links we used (3 years ago) have since died. Hopefully I helped though.
Our problem is we have a handful of dedicated runners without a Facebook account and it's a closed group.
It appears Team Up! might fit our needs, but it doesn't have a way to show attendees. The rest of the features are nice though.
Cozi, Google calendar, search.. There was a site that was pretty detailed (collaborative with different levels of access, color coded events etc) out there but it's been a few years since I tried it. I don't recall the name.
Edit: I believe it was http://www.teamup.com
Note, this is simply something I played with a few times. Use at your own risk etc