The staple of process piping is the butt weld fitting. Typically used from 1" pipe thru 60" pipe size. Grooved fittings have replaced some applications through the years. However, if you have elevated temperatures or want a solid system with very low probability of leakage, nothing compares to the butt weld fitting.
Available in nearly every conceivable metal and in nearly every pipe size and schedule means there is a fitting for every application. Butt weld fittings are made to the same sizing specifications (ANSI B16.9,) so no matter what material you require or which manufacturer produces the fitting, it will be the same size and shape.
Weldbend has introduced a smartphone app that includes all the sizing, weights and other engineering data. I found it very easy to use. Weldbend makes carbon steel fittings and flanges, so that's all that is listed. Add in the 30 other materials commonly available and it would be a complete weld fitting and flange resource. You can find it at Google Play or iTunes store.