The Deciduan™ Couples HUD takes conception (or, if you prefer, breeding) role-play to a new level within Second Life™. It's meant to offer an affordable and accurate alternative to other systems, with a focus on both reality and flexibility to fit many different role-play scenarios. It also integrates with Midnight Lotus, Xcite!, and Aeros genitals, though they're not required, and has several features available to users of RLV-enabled clients such as Firestorm.
The Deciduan Couples HUD is a reproductive system simulator. It differs from similar systems in SL in that it tracks the normal reproductive cycle in both genders, and the odds of conception are highly dependent upon timing. While some parameters differ to accommodate the nature of SL (e.g., transient on-line presence and the general preference of an accelerated schedule), the system strives to mimic real life as much as possible, including the surrounding uncertainty. The realism includes such elements as:
Ovulation occurs only once per female cycle at a semi-random point.
The best chances of conception exist when copulation occurs just before ovulation.
Male potency varies as in real-life; it's dependent upon an ideal frequency (about every two "days")
Female cycles vary in length slightly, often extending slightly beyond the 28-day average. The system doesn't reveal the reason for "lateness" until well beyond the expected end-of-cycle.
That said, there are some key differences from real life:
A "day" lasts four real-life hours. This corresponds to SL's four-hour sunrise-to-sunrise period within any given region. This is configurable.
Ovulation is guaranteed to occur only while you are logged in (provided you do so within your fertile period). Assuming most folks are only in-world once per day, this provides a more-reasonable chance of copulation at the appropriate time.
All pregnancies run to completion unless there is intervention with the Physician's HUD. There are no miscarriages. This isn't for any political or religious leanings on behalf of the developer; it just doesn't tend to be the role-play that our users have desired.
Both men and women are expected to wear the appropriate variant of their HUD. There's also a version that allows switching genders (as is appropriate for some role play).
One word on purpose: the HUD is a role playing tool:
It doesn't get in the way (one small HUD that doesn't take over your screen)
It doesn't do anything it shouldn't.
It won't help you have sex (no "posers" or extra lag-inducing cruft)
It won't tell you what you're experiencing (minimal emotes, and generally private)
It won't leave dirty dishes in the kitchen sink (or clutter up your inventory with extra boxes, landmarks, textures, or crappy gifts you could find at a freebie sim)
None of that. It just adds an element of fairness and mystery between two consenting adults, even if they're role-playing a non-consensual scenario!