One of the things that sold me on using "Stars Without Number" for my sci-fi setting was the "old school" feel to the rules. While I may not be as enamored with some of the mechanics of the pre-3rd Edition D&D rules, I vastly prefer the simiplicity and precieved malleability of the rules. There's not as much there to balance. Really, balance is really secondary to getting what you want out of the system, and I like having that pro-GM feel to the rules. It's one of the main things that I missed when the 3rd Edition rules came out. Really, much of this is a matter of perception, but I point to creature stats to solidfy my point. In 3rd edition games, the stat blocks for creatures greatly grew in size. Not only were there more stats, but so many of the stats modifed other parts of the creature entry. If something was miscalculated or simply missed, the creature wasn't "correct" in terms of the rules. In so many reviews of 3rd edition (and beyond) monster books, so much of the reviews dealt with calculation errors made in the statblocks. That's all well and good, but it got to the point (with me at least) that it seemed like so much of the focus was on the math and mechanics that little attention was placed on the thematics. Sure, a statblock may be complete rubbish, but if the fluff of the creature was good the stats could be fixed.
The simplified statblocks for older D&D games, and especially for SWN, are a big boon. I can easily eyeball and throw together some stats for creatures and NPC's on the fly with a the appropriate level of toughness that I'm looking for. Sure, I could do that with D20 games, but since there's less to SWN statblocks, it's easier and quicker to do. Honestly I'd much rather focus on the "fluff" than the crunch anyway. That's where the real fun of creation comes for me.
Since SWN is inspired (mechanically, that is) by older editions of D&D, I've found myself pouring through my old D&D monster books looking for creatures that would be a good fit in a sci-fi setting. "Conversion" is a breeze. Magical abilities can easily be reworked as psionic abilties or general special abilties. Beyond reworking background information, much of the "work" is already done, which frees up a ton of time to focus on the fluff.
So far, I've been working through the Al-Qadim Monstrous Compendium Appendix. Here are a couple of the entries from a "Xenobestiary" that I'm putting together for my setting:
Dmg: 2d8 or 1d8/1d8 (Bite or Claw x2)
Move: 30’, 40’ Sw, 10’ Br
Ammuts are named due to their resemblance to creatures from ancient Egyptian legend. Ammuts are found on the desert planet of Qadim, The creature resembles a cross between a crocodile, a lioness, and a hippopotamus in mannish form. They have the tail and scaly legs of the crocodile, the tubby belly and thick neck of a hippo, and the sleek arms and head of a humanoid lioness. They are fat, bloated animals, and they are completely oblivious to their surroundings when feeding.
The ammut can attack either with their vicious bite for 2d8 or with two sets of raking claws for 1d8 each. If they bite, their gaping jaws may be unhinged, allowing them to swallow smaller than man-sized creatures on a natural roll of 20. This process is slow and requires 1d4 rounds to complete. During this time, the creature being swallowed is slowly forced into the ammut’s gullet with its jaws and hands. Creatures being swallowed may attack to inflict double damage at a -4 penalty to hit with small, thrusting weapons such as knives or daggers.
In addition to their physical attacks, ammut can roar deafeningly once per turn. All creatures within 20' must make a Physical Effect saving throw or be deafened for 1d10 rounds. The ammut can undertake no other action during the round it roars.
Ammut are equally at home fighting on land or in water and suffer no penalties to attacks when underwater. Their acute senses of smell and hearing allow them to attack normally in the dark as well, but they must make a morale check and suffer a - 2 attack roll penalty when exposed to sunlight or other bright light.
AB: +6/+6 or +6
Dmg: 1d6/1d6 hooves, or 1d12 bite
The buraq are a strange species of equine-like creatures found primarily on Sultus-IV, but some can be found travelling the galaxy with a group of trusted companions. The buraq are dappled grey and white horses with a human-like face. Larger than an ass and smaller than a mule, their coats shine with a rich luster that signals their vibrant health and strength. The buraq’s dappled coat grows more brightly colored on its hindquarters, with speckles of green, blue, brown, and black. Its tail is a long fan of red, green, gold, and blue, with “eyes” like a peacock's tail. Its silverish hooves never need to be shod.
Buraqs are sapient and will observe newcomers for a time before making themselves known. Even though they are sapient, due to their physical limitations they have no technology of their own. Some have been captured and sold into slavery thanks to their inability to truly deal with advanced technology. Some buraq have found passage on starships among groups of off-worlders they trust. While there is little that a buraq can offer a crew in as far as being a crew member, some have found a calling in advising others in matters of politics and business, which it seems they are a quick study.
Although the buraq can serve as a warhorse, it rarely takes any pleasure in such service. When it does serve in battle, it avoids the fray and prefers its rider take a position of leadership without getting entangled in the melee. (A buraq allowing another being to ride it is a sign of great sincere respect and caring for the rider; a boon granted to very, very few.) If necessary, it can strike with its hooves for 1d6 points of damage each or bite for 2d6 points. A foe hit by both hooves is automatically knocked down and trampled for an additional 2d6 points of damage per round until he spends a complete round getting out from under the buraq’s hooves.
Although it is very rare, some buraq have been known to exhibit psionic talent. Most tend to be biopsionics or telepaths, but all disciplines are open to them.
The stats above are changed little from how they appear in the MC, but with just a few tweaks to the background of the creature, and they are good fit for any sci-fi/fantasy campaign. This ability to pull from a vast supply of material made SWN my go-to choice for a sci-fi system. Even pulling in material from D20 sources is rather easy due to being able to eyeball the stats. "Conversion" isn't the chore that it would be with any number of other systems I could have used. Since most of my gaming library is either D&D or D20 System based, I've got a lot of areas to pull ideas from.