FStop.fm connected models to photographers, but if I had to try again, I'd make it the easiest way for businesses to get creative work done. "Project management for creative teams". MVP done, 50k+ users from my original attempt in 2016. I applied to YC twice with this idea.
GuardMyPad.com is a SaaS home security solution built on WebRTC that lets people recycle old devices into motion-detecting security cameras that record media into their cloud storage accounts / local device storage. The MVP for this was finished in 2017, but I never brought it to market because I didn't know how. My mission with this was to give lower-income folks a free way to recycle their old tech into a "better than nothing" security solution.
Karma is a public notebook / collaborative self-education platform (like Roam, but social). I'm using this to internalize a lot of YC / Startup School lectures, eg https://www.karma.fm/p/yINKGvw/how-to-sell-by-tyler-bosmeny https://www.karma.fm/p/vszjKtl/do-things-that-dont-scale---paul-graham
CondoGrades is meant to give power to residents/owners who have fallen victim to incompetent HOAs / property management companies / abusive landlords. It would begin as Yelp for condos - "get paid to grade your HOA". Renters and homeowners would get paid to provide data that CondoGrades sells to home buyers / real estate agents. Landlords would pay for the ability to respond to public renter feedback.
Tweet.fm is a voice-based twitter alternative built on subscriptions (no ads).
Rolo is an omnichannel CRM solution - connect your Rolo account to all social media + email channels, and have one place to communicate with customers on whatever channel they prefer (Twitter DMs, emails, Facebook messages, etc).
Kanban is like a public Trello that allows people to contribute to projects via small tasks, and get paid for closing out those tasks. "Public project management" positioned to support the growing needs of decentralized projects. (PG's talk on "solving email" by treating it like a TODO list is what inspired this - step 1: forward emails into a spam-detecting Trello-like interface so you never have to visit an inbox again, step 2: evolve from private, personal task management to collaborative project management).
Docs.fm is a simple docs-tracking utility that automatically reminds product teams to review / QA / sign off on their technical documentation. This is a huge problem for product teams - technical docs tend to go stale because our systems don't make it easy for PMs / EMs / SWEs to form a healthy documentation habit. Docs.fm is the habit-forming solution.
Unionite is a universal unionization platform / "nonviolent resistance as a service".
BitSpend is a simple tax calculator for crypto holders who spend their holdings and need an easy way to calculate their cost basis / tax liability. It just needs your public wallet address(es) and your income bracket. Then, you tell it when you spend, and it spits out the lowest possible tax liability based on when your crypto was purchased (first in, last out to minimize tax). All in a format that's easily attachable to your state/federal tax returns.