If you have tried to build out a whole-home smart home solution or tried to create complex home automation in HomeKit, you will likely agree that HomeKit is — to put it politely — lacking in some areas.
Whether it's support for a device you already own or want to purchase, an entire device category, or "complicated" automations like turning off a light switch automatically after a timeout, HomeKit can be frustrating for those who want to bring automation to every aspect of our homes.
Fear not, though, there are several ways to extend HomeKit to make it the home automation platform Apple would like to think it is.
Homebridge, HOOBS, and Starling Home Hub

Let's start with the most well-known option, Homebridge. Homebridge is an open-source platform that exposes a software-based HomeKit-compatible device hub1Note: some device categories create their own hub or are exposed directly to HomeKit that exposes any number of devices that HomeKit doesn't support so you can control them from within HomeKit. At the time of writing, Homebrige has more than 2,000 plugins, which are contributed by its vibrant community of users thanks to its Javascript-based core.
Homebridge can be installed on almost any hardware, including the ever-popular Raspberry Pi with its tiny power consumption for what should be an always-on device — but any old laptop or desktop running macOS, Windows, or Linux will work just fine.

Read more of our coverage of Homebridge here.
Homebridge itself is free (as in beer, although it is also free as in speech, too!), so the only actual cost is your own time and any hardware you choose to buy.
HOOBS
HOOBS, or Homebridge Out Of the Box, is a pre-packaged solution for Homebridge providing a customized Homebridge pre-installed on plug-in hardware. Hoobs is $219.99 for their starter kit.
While Homebridge installation isn't challenging, HOOBS is a great way to get up and running as quickly as possible for those who want a turn-key solution with support for most-if-not-all of Homebridge's 2,000+ plugins.
You can also buy a pre-flashed microSD card for $24.99, which you can insert into any supported Raspberry Pi if you happen to have one lying around.
Starling Home Hub
The Starling Home Hub is another Homebridge-based product; however, unlike the minimally-customized HOOBS, Starling Home Hub is a heavily customized solution exclusively for supporting Google's Nest products.
If you have many Google Nest products already, this will save you from having to replace them all if you want to migrate to HomeKit. At $99, it does one job and does it well. However, you will still need to continue paying for your Google nest subscription.
Scrypted

A relative newcomer to the HomeKit scene, Scrypted is similar to Homebridge — open-source, Javascript-based, exposes unsupported devices to HomeKit — however, it is an entirely separate project primarily focused on security camera (and video doorbell) support. It also supports Google Home and Amazon Alexa platforms, not just HomeKit.
Scrypted was the first open-source project to add support for two-way audio and HomeKit Secure Video (HKSV). It is arguably this, alongside its excellent support of the popular Ubiquiti UniFi line of security cameras, that has resulted in a surge in popularity of late.
In particular, given the dismal state of HKSV doorbells has led to many folks looking outside of the native HomeKit system.
Home Assistant
Unlike Homebridge and progeny, or Scrypted, Home Assistant is not an extension to an existing smart home platform (HomeKit or otherwise) but a fully-fledged smart home platform. Home Assistant is arguably the open-source smart home platform and a must-have for anyone who wants to create an entirely private whole-home smart home setup.
However, Home Assistant doesn't have a built-in voice assistant, so it's common to pair it with an existing smart platform. Home Assistant has built-in support for Apple HomeKit, enabling it to expose its supported devices to HomeKit like Homebridge or Scrypted.
Home Assistant has almost 2,000 integrations, bringing it on par with Homebridge. But, of course, there isn't complete overlap between the two ecosystems, with some devices only supported by one or the other.
The main benefit of Home Assistant is its robust, flexible, and incredibly powerful automation capabilities; it is often easier and more reliable to create more complex automations in Home Assistant and expose them to HomeKit than to do it natively in HomeKit.
My Setup
Like many HomeKit users wanting to expand device support, I started with a Homebridge install, primarily for dummy switches for automation and its LG ThinQ plugin that works with my fridge/freezer and my washer/dryer set.
However, to bring my new GE Profile Range to HomeKit, I installed Home Assistant with the SmartHQ integration. I also created some custom automations that would ensure we don't accidentally turn on the oven but allow us to view the oven and stove status and set a reminder light to prevent either from being left on. We can turn it on or off using Siri but only when explicitly called (and not when we ask Siri to turn on/off the kitchen). I have also switched (pardon the pun!) to using Home Assistant for my dummy switches, as they are now the primary interaction point between Home Assistant automations and HomeKit automations. I have moved over all my integrations except for the unavailable original LG ThinQ support.
Lastly, as I have gotten fed up with native HomeKit security video options, I decided to explore the Ubiquiti UniFi Secure cameras as I already have the rest of the required hardware. While both Homebridge and Home Assistant support the devices, Homebridge was late to the game with HKSV and seemed less reliable. Additionally, Home Assistant doesn't support 2-way audio or HKSV, so I have recently introduced Scrypted.
My UniFi cameras load as fast or faster than any HomeKit native camera I've tried, and even those that don't have native AI detection gain those features through the HKSV connection. My G4 Doorbell also performs better than my previous Eufy (non-HomeKit) and Logitech Circle Doorbells, with instant notifications, two-way audio, and even features like zones and package detection.
All three of these systems run on a single Raspberry Pi 4b (8GB), with plenty of CPU and memory to spare, despite running four security cameras and a doorbell. I will be adding four more cameras over the next week, and I don't expect any issues.

I plan to move all of my existing automation to Home Assistant and as many devices as possible, making HomeKit merely a nice frontend with a mediocre (at best) voice assistant.
Final Thoughts
HomeKit is a great platform with some frustrating limitations, many of which we accept as trade-offs for better privacy and security. However, with help from the open-source community, we can expand on HomeKit to enable far more complete and much more sophisticated home automation and device compatibility.
- 1Note: some device categories create their own hub or are exposed directly to HomeKit