What are the best Open Source alternatives to popular SaaS?

https://awesome-selfhosted.net/ is an excellent starting point to find projects that might suit your needs.

Are there any specific providers' products you want alternatives to? Most of the ones I use are hosting open-source software that I could host myself, if I wanted, but it may not be so for your use.

for example:

netlify, render -> coolify

zapier -> n8n