Neo Euler is available under the SIL Open Font License:
It is an Open Type version of the AMS Euler font:
I'm closing all these font-specific meta bug since the main work has been done in bug 407059 and bug 947650. Remaining issues will be handled on the OpenType MATH bugs.
Once bug 1000879 is merged, one will be able to verify the initial OpenType MATH support with the MathML torture test: