I would argue that even in the age of the app, a domain for your side project is still absolutely important. Now, despite that, one of the truths of side projects is that your domain is important but you aren't going to be dogmatic about it in the way that a funded company approaches their naming.
What I like to do for this is figure out possible options and then run with a multiple domain search service. I'm playing around with a project which has a couple of possible related keywords in the domain:
This gave me a bunch of combinations:
safechat.com safechat.io safetalk.com safetalk.io soberchat.com soberchat.io sobertalk.com sobertalk.io safetexts.com safetexts.io sobertexts.com sobertexts.io safetexting.com safetexts.io
A quick trip to octopoly and their search engine:
let me put in a bunch of these and find out which are available domains. I didn't end up with exactly what I wanted but I did end up with a good enough domain which was sufficient to move forward – and that's generally enough for a side project.
Octopoly. Absolutely recommended.
Note 1: I'm sure there are other options out there and ones that do automatic suggestions, etc. But the ones that I've seem are paid and none seem to work quite as well as Octopoly.
Note 2: Do not register your domains thru Octopoly, their costs are insane. A .io domain is normally $39 when bought through AWS but it is $79 through Octopoly. Grumble.