A medical device startup, based on a technology platform I invented in grad school. The startup part is what started me hanging out on HN, but I've found that there is very little overlap between what I'm trying to do and what startups on HN do. Still, things are interesting enough here that I keep checking in.
edit: I missed the "how's it working out?" part.
Not great. Cash starved from day 1. Funding for medical devices is quite, quite different than software (i.e., bad but getting better recently). We don't fit the model for many VCs, so that limits potential sources, and being in medical devices means that we need to deal with sophisticated investors that can run proper DD on us, further limiting potential sources. Funding has been (and still is) a struggle! It's also a little bit "lonely": we run into a lot of problems unique to this industry, but often we can't talk about it in detail, and even when we can, there aren't many people around to talk to.
Project management has been interesting. There's quite a number of consulting and industrial design groups out there, which helps to bring in expertise when needed and keep things lean overall. A big challenge has been in setting up the supply chain: it's not something I've done (or thought of) before, but consulting has helped out here as well. Basically, we'd be dead in the water without outside consultants.
Regulatory affairs is a pain, but I appreciate why it's there and it's not onerous per se, just slows everything down (not necessarily a bad thing). It more or less distills down to documenting "say what you're doing, and do what you're saying".
The technology side is a bit boring, honestly. We need to design things conservatively, unless we have a really, really good reason not to. We also need guaranteed years of availability for parts, which additionally tends to lead to conservative designs.
Surprising lessons learned: cable management (i.e., in the device) is a nightmare, and packaging is anything but a simple problem to solve. Also, may have learned more in 6 mos. tilting at these windmills than my entire undergrad + graduate career.