There are several good alternatives to black pipe fitting:

Galvanized steel pipe.

Galvanized steel pipe comes with a zinc coating that helps prevent rust and corrosion. It offers longer lifespan and durability than bare black pipe. Galvanized steel pipe fittings like elbows, tees, unions, etc. can also be used in place of black pipe fittings.

Stainless steel pipe.

Stainless steel pipe is extremely corrosion resistant and durable. Stainless steel pipe fittings provide the best performance in corrosive environments or for high-pressure, high-temperature applications. However, stainless steel pipe and fittings tend to be significantly more expensive than black pipe.

Copper pipe.

Copper pipe is soft, durable and highly corrosion resistant. It offers excellent performance for potable water supply lines. Copper pipe fittings, like ells, tees and joints, can be used in place of black pipe fittings. However, copper pipe and fittings also tend to cost more than black pipe alternatives.

PVC pipe.

PVC or polyvinyl chloride pipe is easy to install, chemical resistant and durable. It is a good alternative for underground supply or drain lines. PVC pipe and fittings are relatively inexpensive, lightweight and UV resistant. PVC is suitable for low-pressure applications only.

CPVC pipe.

CPVC or chlorinated polyvinyl chloride pipe shares properties similar to PVC but offers higher heat and pressure resistance. It can withstand temperatures up to 200 F. CPVC pipe and fittings are a good alternative for black pipe in high-heat plumbing applications. However, they also tend to cost a bit more than PVC.

Schedule 80 PVC pipe.

Schedule 80 PVC pipe has stronger and thicker walls than regular PVC pipe. It can withstand higher pressures and temperatures. Schedule 80 PVC pipe and fittings can serve as an alternative for black pipe in more demanding applications compared to standard PVC. But it is also more expensive.

Recessed-flange cast-iron fittings.

For high-pressure, high-temperature steam lines or other critical applications, recessed-flange cast-iron fittings provide an excellent alternative to black pipe joints. They are durable, strong and able to create a foolproof seal, but cost is significantly higher. They are rarely used for general plumbing supply lines.