We got engaged while Jess was in San Francisco for an internship, which meant the first few months of our engagement were spent apart. Our schedules rarely lined up: one of us was available in the evenings, the other was a little more flexible in the mornings.
Slack
We ended up adopting a system of communication that worked from different states, and that could also be shared with other collaborators (our parents, members of our wedding party). Ryan all but demanded that we use Slack, which was still relatively "new" at the time. This became a depository for documents -- quotes and bills for various vendors, price sheets or details for food trucks and alcohol distributors, etc. Slack, unlike traditional texting, allows for searching through all content ever posted. (You don't have to constantly reload outdated posts.)
One of us is still a little skeptical about Slack in non-business contexts, but that person will also admit that it was super helpful to have a text-searchable Dropbox folder of files with additional conversation-style context around each. If Ryan needed to compare prices for two dessert vendors, but I'd been in communication with one of them, he could easily search for the name or topic of that vendor to find their original quote.
Sad note: We will not be providing Short Leash, so don't get your hopes up.
Quip
Our other method of communication ended up being a huge help for multi-person collaboration, and for keeping everyone on the same page.
“Quip is a collaborative productivity software suite for mobile and the Web. It allows groups of people to create and edit documents and spreadsheets as a group, typically for business purposes.”
Jess uses Quip extensively for her work, so we created a shared folder (Mawwiage, obviously) where we could upload files or create collaborative spreadsheets and documents for planning.
Our biggest document is, of course, our massive Wedding Checklist, which builds off recommended timelines from sources like Brides, The Knot, and Wedding Wire. It's probably the key document that has helped us maintain sanity: Whenever we find out just another thing we'll have to take care of between now and May 13 (e.g., delivering welcome baskets to hotels; sending final guest list to food truck; picking up kegs from Taste of Tops), we just add it to this checklist and take things one week at a time.