I have no affiliation with any the following tools. I have used most of the following recommendations personally and been referred to the others repeatedly. Please do not Google things like "Best accounting tool for startups" as it is SEO affiliate content 99% of the time. At the bottom of this article I am including a link to some of the most helpful resources I've found from top angels, incubators, and VCs.
Legal
General
Recommendation: https://www.avodocs.com & https://www.clerky.com
Avodocs has a bunch of standard free startup legal templates. Clerky has a bunch of helpful blog posts, as well as a subscription legal offering to make getting customized legal advice cheaper.
Incorporation
Recommendation: https://stripe.com/atlas
You can spend $1,000s of dollars talking to lawyers about this or you can simply use an excellent template and filing platform to start a C-Corp or LLC. It barely costs more than self filing with the government, plus you'll probably end up using Stripe to handle subscription payments and invoices to customers so it doesn't hurt to have it all in one place.
Don't forget to file your 83(b) if you go the C-Corp route. See what Clerky says here
Founders and Equity
Recommendation: https://www.ycombinator.com/library/5x-how-to-split-equity-among-co-founders
If this situation is hairy for you all, it likely will stay that way for the life of your company. Make sure everyone is totally happy here.
Investors
Recommendation: https://www.ycombinator.com/documents & Venture Deals
The SAFE is standard for venture backed startups. For in depth fundraising info, download the PDF of Venture Deals below. I read Venture Deals cover to cover, then used it as a reference extensively during the formation of my company. Thanks for the recommendation Andrew!
Finance
Accounting
Recommendation: https://www.lucahq.com
Luca will give you fractional accountants and save you a bunch of time and money when it comes to bookkeeping. They can likely share advice with you about the best accounting software platforms to use, though they may have a vested interest in what they recommend.
Banking
Recommendation: https://mercury.com
Don't use a local bank. And don't use Silicon Valley Bank - it's a misleading name for a very outdated bank.
HR
Overall
Recommendation: https://www.rippling.com
There are a lot of products out there. Rippling makes it dead simple to hire employees and contractors. In many cases it will automatically allocate new hires Google accounts, connect to any SaaS tools they need, then automatically deactivate those accounts when they leave. It also has an extensive marketplace for cheap healthcare. We were able to find healthcare for a founding team of 2 that cost us less than our previous corporate health insurance policies.
Foreign Contractors
Recommendation: https://www.deel.com
If you have a direct relationship with freelancers and contractors abroad, Deel gives you a cheap method to pay them through a local, corporate entity in their local currency while paying in USD. If you work with a foreign agency like Toptal, they might be upcharging as much as 50%, so it usually is best to have a direct relationship with the freelancer.
Hiring Contractors and Engineers
If you want to understand the landscape here, I'd be happy to give you an overview and help out. Shoot me an email at j plus 3 plus e plus lam at gmail.com
Trusted Resources
https://www.ycombinator.com/library
Missing something?
Feel free to email me! I'm always happy to meet new founders. Shoot me an email at j plus 3 plus e plus lam at gmail.com