For an incredibly easy to use platform to send beautiful emails to your community, Flodesk is the best I have found by far (and a startup by womxn!). Get 30 days free and 50% off for life.
To create a gorgeous and simple experience for your clients my answer is Dubsado. Takes a bit of setup, but once you're up and running it's fantastic. First 3 clients free and get 20% off your first month or whole year.
I don't use Acuity anymore but it's a brilliant and simple place to start when you book clients in your business. There's a free plan but I had the $10 a month plan which is awesome. Slick and easy.
Trello has simply been a life-saver for me! I have tried ALL the ways of organising my life and my work, lists, software, notes apps, your name it and keep coming back. I bloody love Trello and use it daily!
I've been a Canva user since the get-go and I love it just as much now as I did in 2015! Easily customisable templates, upload your brand fonts and images and so flippin easy to use. 10/10 recommend.
I started my business using Skype but soon discovered that Zoom was easier to use, more reliable, has the ability to (easily) record calls and is great for group calls. I haven't looked back since.
Not only does G-Suite host my email domain (linked to my biz URL), I also get the full suite of Google cloud-based apps and 1TB of Google Drive storage. I couldn't be without these apps now.
Yes I can't help myself, I've been a Microsoft Office user for soooo long (I even taught it years ago), that I can't let it go. Google Docs are brill but sometimes you need something more!
I love Moo.com, their stationery quality is without doubt the best around for an "off-the-shelf solution. I especially like them for those extra touches like stickers and branded envelopes.