Gauss weapons are meant to be an alternative to starting tech for laser weapons, with a different profile but roughly comparable and also available from the start. The main reasoning behind this decision is that both real life hand-held lasers and hand-held railguns suffer from the same problem: it is impossible to build a power supply compact enough to make the weapon practical. If we assume that this problem was overcome for the lasers (probably thanks to early research on alien tech), then we can make gauss weapons too.
The mod adds the following items:
1. Gauss Pistol. A powerful, weighted side arm.
2. Gauss Rifle. A hypervelocity kinetic weapon, very effective against lightly armoured, big targets.
3. Gauss Sniper Rifle. A natural development of the Gauss Rifle, sacrificing mobility for greater accuracy and even more damage.
4. Heavy Gauss. Makes big holes, easily comparable to plasma weapons (at least when pitted against enemies with low resistance to Armour Piercing), but much more unwieldy.
5. Gauss Tank. A standard tank with a slightly modified Heavy Gauss.
6. Gauss Hovertank. As above, but mounted on a hovertank chassis. Has far greater mobility and thicker armour, but at a cost of less efficient snap shots (stability issues). Both require gauss ammo rounds to be used.
7. Gauss Cannon. This craft weapon has shorter effective range than the Laser Cannon, but it packs more power per shot (the rpm value is similar for both weapons).
8. Railgun versions for all the above.
It also adds relevant research projects, manufacture orders and Ufopaedia entries.
Most of you are probably wondering about the TFTD gauss weapons. They are irrelevant: these gauss guns have different stats and a different role. They are more powerful and more accurate than lasers, but they lack autofire and their damage type is Armour Piercing, which most aliens are more resistant to than to lasers. They require ammo clips, but the clips are generally large (since gauss bullets are fairly small). (TFTD gauss guns didn't seem to have anything to do with gauss weaponry whatsoever, but that's beside the point.)