Femmecup is a silicone reusable menstrual cup.  Used internally to catch your  menstrual flow, it's a great alternative to tampons and very cost effective.  The Femmecup will hold about 30ml of fluid, which is about a third of most women's entire menstrual flow, so is suitable whether your flow is heavy or light.

Uniquely, the Femmecup is a "one size fits all" menstrual cup, it is 45mm wide at it's widest point and 50cm long (including the stem, which you will most likely need to trim).