Here is a template for a versatile melee build that uses crossbows, traps, grenades and also has PSI support that you could easily remove/ignore but I would not recommend it.
LVL 10
https://underrail.info.tm/build/?CgMHBwMDAwYAMjw8AAA8AAAAMgAUFAAAACgAGQAAACsmORkWKjgw378Notice 10 unspent ability points. You will use those depending on what weapon you choose.
You can craft Shock Bolts and Molotovs, have PSI abilities Limited Temporal Increment, Force Field and Electrokinesis. Buy Tabi Boots. All of these you can get from shops and trainers as SGS and another town you visit during "tutorial".
With Premeditation+Electrokinesis and Special Tactics+Shock Bolts, you can stun 2 enemies at the start of the fight and do some nice AoE for 0 AP. You can wall yourself with Forcefield, when it expires you will go first again, effectively gaining 2 turns at the start of the battle. With Grenadier and Limited Temporal Increment you can throw 2 grenades in the first two rounds. You can place bear traps in combat to create choke-points. Then just mop up with basic melee attacks.
When you finish SGS missions and world map opens up you can find/buy the other two important PSI abilities relatively soon (Electrokinetic Imprint and Psycho-temporal Contraction). The last PSI ability, Stasis, comes much later.
LVL 30
https://underrail.info.tm/build/?HgMHBwMDAwYAMkvCoAAAwqAAAAAyABQUAAAALQBGAAAAKyY5GRYqODASBkvCo8KzImrio7EF37814 free ability points and 3 free feats between Quick Tinkering and Increased Dexterity (that you actually take at level 26).
Pick a weapon, fill the weapon feat and STR requirements and pour the rest into DEX, or put a point or two into CON if you don't want to be paper-thin. Ignore defensive weapon feats, you are playing to not get hit at all, also all RNG based defense sucks. Be sure to check the wiki Dexterity page for AP reduction on light weapons (knives and unarmed / fist weapons).
Expose weakness in mandatory to deal with super tanky enemies, Cheap Shots and Critical power are general damage increase abilities, and Versatility is there to raise crossbow skill. The last two feats are Marksman and Elemental bolts (level 28&30), at that point in the game you should have good gear and you can even play this as Elemental CB build, just spam Shock Bolts, Premeditation+Electrokinesis, stun everything and mop up with melee or grenades. Other elemental bolts are great too. Every melee weapon can work with this but unarmed (pure unarmed) and knives are much weaker than fist weapons and hammers. I don't have experience with spears, and swords are by far the best.
Specialization points only Quick Tinkering AP reduction is mandatory, the rest spend on CD reduction of important abilities or just pour everything into Critical Power/Versatility.
For gear Infused Rathound Leather Armor, Tabi Boots (check the wiki page and pick infused leather that has a bonus you like, does not really matter), Doctors/Lifting/Quiver belts as situation demands, best energy shield you can get your hands on, Blast Cloth Balaclava/Seeker Goggles, melee weapon of choice and crafted crossbow.
I don't know if you played the game so I didn't want to spoil anything, there are a lot of things that raise crafting, lockpicking and hacking, and also they are synergies to each other so I left that part for you to figure out as you play, or just check the wiki and forums and play around. If you want I can post finished build.