I've been modding GTA 4 and 5 with LSPDFR since I found this - really enjoy doing it for the past few years. I'm a software engineer by trade. I've had some more time become available and I'm interested in starting to create some of my own callout packs - I'm not much one for developing cars and skins. However, I want to contribute back to the community, and I think that's the best way of doing so. This might not be the correct forum, if not could you point me in the right direction. Two questions that I have for the current modders:

 

1. Why aren't more things like callouts open sourced via GitHub to allow the community to contribute? Does this model for development work? Has anyone been successful at doing this?
2. What resources are available for development (i.e.: documentation about the API, IDE, language, etc)

1) No idea. Toasty Callouts (which is what I am currently working on) was open sourced for a little while, but I gave up on trying to teach myself to commit/push every new feature I added. Just a hassle imo. May re-open source it down the road.

2) 

http://www.lcpdfr.com/forums/topic/64702-api-development-hub-information-resources-guides/

http://www.dev-c.com/nativedb/

https://rphdb.com/native/

https://github.com/LMSDev/LSPDFR-API

http://ragepluginhook.net/Documentation.aspx

Check this out