Whats the difference between ESP-WROOM and ESP-12?
ESP-WROOM is manufactured by Espressif and ESP-12 by AI-thinker i believe. There is same ESP8266 chip on those boards.
In the mean time I got an answer from Espressif. Both seems to be identically. I had the hope that the Flash is bigger then 4 MB. But, its thesame size.
Most of these boards (esp-01, 07,12,12E etc) are identical apart from pinout variations and more or less FLASH. It’s down to what is useful to you. You might want 0.1" spacing or minimum size or internal/external aerial etc… at the end of the day, the controller chip is the same.
@Martin_Smola From data sheet (Jun 2, 2015):
This module is mounted with an 4 MB external SPI flash to store user programs. If larger definable storage space is required, a SPI flash with larger memory size is preferred. Theoretically speaking, up
to 16 MB memory capacity can be supported.
@Peter_Scargill For the use of NodeMCU more Flash would be helpful. The Olimex board has 16 MB which helped a lot. (http://ckuehnel.ch/dokuwiki/doku.php?id=nodemcu).
But internal RAM of the CPU is the limit, I think.
Yes in all cases the internal RAM is more of an issue than FLASH - it would have been nice if we’d had more - however it is still possible to do quite large projects with the amount of RAM available…
We were just about to when we discovered another bug 
I understand my colleague Aidan back in the UK has just got a new load of bare boards and is putting one together. Email me pete at scargill dot org and I’ll pass the request on.