Besides the balanced sword and the featherweight axe, what other melee weapons can you make with a technologist and how good are them?
I already know about the pyrotechnics axe (which is truly devastating) and the charged axe (I still can't make one... is it any good?).

Going from memory here, so some of the names and details might not be accurate:
Mechanical Dagger - Better than the other daggers I can recall, but still not that useful.
Machined Hammer - Don't bother.
Shocking Staff - Standard staff with a small amount of added electrical damage.
Charged Sword - Balanced Sword with additional electrical damage, possibly slower.
Charged Axe - Very effective. Decent standard damage coupled with powerful electrical damage. Not as good as Pyrotechnic Axe.
Envenomed Sword - Fair bit of poison damage, but little else.
Envenomed Axe - Like the Envenomed Sword, but slower and more damaging.
Power Axe - I don't think you can actually make this, but it is effective as an early to mid-game weapon.
Apart from the ones you mentioned, I can't think of any others.

That Charged Sword is a little bit slower but it's fantastic. Later in the game I gave one to Virgil and he and I were kickin' ass.

I have tried the charged sword... while the pyrotechnic axe is still the most powerful melee weapon I have seen in the game, the charged sword is awesome as it's strength requirement are far lower than the axe and it deals huge damage none the less.

pyrotechnic axe, 1-20 DAM and 30-50FD!!!!!!! Gave it to a NPC and hes beast body parts everywhere! mwhahah lol.

you can buy the schematic from a vendor in tarant, the blacksmith dwarf
feather weight axe+ fuel, only 20 BS skill and i think 10 EXP required, slower weapon like 5/7 but the npc still gets 2/3 swings per round, plus he has a shield.