I know you're asking about developer tools - the main ones I use include:
* Webflow (in case the client needs something relatively unsophisticated)
* Django / HTMX / AlpineJS / Django Ninja (in case the client needs a full CRUD application with more powerful capabilities).
I also want to shamelessly plug - if you are looking to do freelance or contract work, and you want an easy way to manage the contract, engagements, milestones, and invoices, consider using withpartly.com.
I'm the founder and CEO, and looking for freelancers / contractors to play around with the alpha product (for free).
If you do opensource it, happy to help maintain it. This product would be helpful for my (fledgling) company, but would need to be self-hosted (use case is esignatures)
I'm creating software to make it easy for freelancers to manage their engagements, get paid, and handle all of the pieces of paper involved in that (NDA, IP assignment, etc). As part of that, I'm working with companies looking to hire contractors, specifically software engineers.
If you're looking to work with Series A / B companies as a software engineer for at least 10 hours a week (either in contract to hire or in permanent freelancer setups), please reach out! The main cost to you is you'll have to use my software and give me feedback on it. Thanks!