Econo JIT is largely a dead concept. The idea is there were to be three
JITs. Econo JIT was one that JITTed on the fly very quickly. The standard
JIT was used in most cases, while the Opti-JIT (optimized JIT) was designed
to optimize the output. It was a nice idea, but never came to full fruition.

In ASP.NET 2.0, there is JIT on the fly, which is as close to the concept of
Econo JIT you come to. The standard JIT is there and the Opti JIT is largely
ngen.exe.