Kimai
The price everyone charges for time-tracking is insanity when Kimai is available. I self host this behind a cloudflare tunnel and it's the easiest $20/month we save. I've even seen it available on CPanel, managed hosting installations. It's a no-brainer for a freelancer.
Flame Dashboard
When you have a network of contractors and a bunch of cobbled together services, this self hosted dashboard helps keep things straight.
Twenty CRM
I tried to self host this unsuccessfully, I'm a poor-to-moderate IT guy so I've happily started paying them to manage. Having an affordable, easy CRM has been so helpful. I have less than 100 contacts in there right now but with my small business don't need many more.
N8N + Baserow
I use N8N for a few CRM automations, some social posting and experimentation (how about an Adobe Media Encoder node?!) but the star of this show is an app I made called SendIT.
Using templates I create on my Ghost blog, I've created a grip of custom emails I use when sending things to clients. I have templates for download and review links, delivery of assets, pitches and package tracking numbers. N8N runs the backend, Baserow made it easy to create a front-end. Highly recommended.
Bookstack
I've put a ton of our information that gets re-used by producers and contractors into a private wiki. Travel details, processes, model release templates, everything in one place.
Nextcloud
What a pain the arse to setup! But now that it's working it powers our shared project files. Mainly between editor and assistant editor, I don't trust it to share files with clients (I use Frame.io and my Synology NAS) but as a central place for project files, coupled with rsync automated backups - it's brilliant!
Uptime Kuma
With all of these services, it's good to make sure they're up and alive. Uptime Kuma is excellent to ensure uptime. Coupled with notifications, I feel good that I'll catch anything that goes down. I've also run into having my portfolio down when a client was trying to access it, a nightmare. Uptime Kuma is that security that everything is working.
Cal.com
I don't self host this but, what an incredible piece of scheduling software. I hate booking meetings, making invites, the whole deal.