Ignition ERP system

Has anyone developed an ERP system in ignition that they are willing to market or share?
We are trying to decide what direction to go in developing our own or integrating to a 3rd party system.

Yes, take a look at SepaSoft.
Their MES module used to be sold on the IA website.
There are a couple of others out there with specific focus.

I worked for a company that had a home-grown ERP system, so I can talk about it a little. The benefit of building it in-house is you have full control over the entire system and you can build it in a way that makes sense for your operations. One of the intimidating things about an off the shelf product like SAP or Netsuite is they have so many extra features that aren't needed a lot of the time, so it makes the process of using them overwhelming for beginners. If you build it, it will be custom to your process and industry.

The downside of building your own ERP is that you have full control over the entire system (and, consequently, full responsibility). This can get complicated very quickly, especially if you're in a regulated industry.

I think a reasonable thing to expect is ongoing development and support for many years. Even if you deliver a feature-set, you will undoubtedly get feature requests (because some users may be coming from other ERPs or there is a need for more functionality). We had 2 developers working on our system on and off since about 2015, both new development and bug fixes/improvements. This will be different for you, but that is one case study for you to consider.

In my humble opinion, it is probably not worth the effort in most cases to build an ERP from scratch in Ignition - what you should look for instead is a system that has many integration options so that you can connect to the ERP from Ignition and get more functionality that is tied in with your broader Ignition system (what I mean by integration options are database drivers, REST endpoints, etc). I believe the additional cost of the ERP licensing and support is offset by the development cost of building and supporting/maintaining an ERP from scratch.