We're launching an app in 2 months and would love to build a waitlist of 5000+ people to fundraise as well, so looking for good growth hacks!
If you are asking how to do it technically then you can use any of the web page development services (e.g. Wix) and add a form that is linked to a list service (e.g. MailChimp).
If you are asking how to attract potential customers and persuade them to submit the form then there are a number of things to try.
To attract them, you can use paid ads or organic (e.g. Facebook/YouTube/Instagram text/video posts given that this is B2C). The ads/posts must address users' pain/need/desire and show that you will solve this. Ideally, offer some value (useful insight etc.) in the ad/post to show you really can solve it.
To persuade them to sign up, again, the page should remind them of the pain/need/desire and how you can solve and ideally offer immediate value (e.g. white paper) when they register (as well as future promise of an app they might have to pay for).
Also, if you can think of a way of giving additional value for referrals that will help.