Almost every single job I've ever gotten is because of a side project or because I incorporated a small company to legitamise a side-project I was hacking on.

Over the years:

I built a video capture system for the Commodore Amiga as a neat side project for that lead to me working on Transputers that formed the heart of a non-linear editing system (no interview)

The Transputers were really fast, so I wrote some neat 3D demos that ran on the Transputer boards in the Amiga & PC => contract work with SGI (no interview)

Wrote a demo for the SGI video capture system to scan a magazine at high resolution => machine vision & robotics that was changing the printing industry (no interview)

Wrote a C compiler for an 8-bit micro so I could learn C => leads to writing a C compiler for a 16-bit micro at a company (no interview)

Created a "smart home dashboard" for a side-project => leads to writing a mobile app to manage a WiFi router => leads to becoming Lead Firmware Engineer on the project (no interview)

I wrote some stuff on the Unity3D forums => game development job offer (no interview)

Ran a number of in-person developer meet-ups over the years => various jobs & offers & contract gigs (no interview)

Got asked by a friend to teach a class on device driver development at USC, video recorded it, he sent it to his friend at Intel => wind up teaching many, many week long, rocket-science level classes on Linux & Android & device driver development & board bring-up at Intel (no interview)

Recorded all of my lectures at Intel, shared them with a friend at Facebook who was trying to get in to device driver development => Which lead to me teaching a couple of classes at Facebook (no interview)

Asked to critique a ReactNative class at Facebook due to my other teaching there => Which lead to me consulting/contracting for Facebook for a few years (no interview)

Video tape my classes at Facebook, which get shared with people at Microsoft & Apple without my knowledge => end up consulting and teaching at both Microsoft & Apple (no interview)

Created a bot for a popular MMORPG coupled with machine vision and some AI techniques => contract job to detect bots in the self-same popular MMORPG (no interview)

I created a C# package and published it that done some fancy stuff with random numbers => company hired me to work on their project that used the library (that was an "interesting" interview)

I wrote some SONY PlayStation developer tools => leads to getting a job at a game development company creating a PSX game (no interview)

Create some tools to theme websites and pull data from a database => accidentally create an adult entertainment empire (no interview)

Document how the Gameboy works, write some developer tools, maintain some developer tools => multiple jobs developing Gameboy games (no interview)

Port MAME to a bunch of consoles, write emulators as side-projects for other consoles => hired to write emulator of their classic consoles for "big console development company" (no interview)

Hacked on some gstreamer code => connection with a guy at a Canadian who says "if you're ever looking to move to Canada..."

There's lot of other examples in my career where building a side-project leads to an interview or a straight-up offer.