Normally this is spam, but this is likely being posted because the job location is San Francisco and that salary is hilarious.
Of course 5% equity isn't peanuts if you really believe in the company... and if your equity comes in a form that's protected against them diluting you to hell.
If I were to even consider such a position I'd involve a lawyer in examining the equity part, and I'd really have to believe in the company.
CrystalMD would do better to offer $1/year for this job, since what they are actually looking for is an angel investor whose capital happens to come in the form of engineering time.