Intro
Messing around with Pinguino (and thinking about the most popular 8bit boards, designed for breadboard mounting) I found that it could be interesting designing,
• a new board with Arduino format, to be physically compatible with its shields
• with two IC sockets, allowing to interchange both 8 bit micros available (18F4450 and 18F2250).
After several trials, here is Pinguino mm8; a simple development board that meets both objectives.

In case anyone else is interested, I share it here as OSHW (Open Source Hardware), so anyone can use or modify it under CC-BY-SA 3.0.
Versions
1.10

- RA3 pin is now connected to AREF to improve compatibility with shields requiring it
- VUSB connected to GND (on the first version was mistakenly disconnected) including a 220nF capacitor
1.00

Notes
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Micros
Although both micros are supported (18F2550 y 18F4550) mm8 is not designed to mount both of them at the same time.

Ref: PIC18F2455/2550/4455/4550 Data Sheet.
LDOs
mm8 uses two LDO regulators 1) to adjust the external input to 5V and 2) to feed the 3V3 pin that some Arduino shields need. Any SOT-223 LDO will work, but I suggest you to test the MIC391XX series from Micrel.
Ref: MIC39100/39101/39102 Data Sheet.
Pin Mapping
The front silkscreen contains the Arduino-style pin notations and the back has the microcontroller pin nomenclature.
Anyway, here you have a list with the signal pins mapping (including also the standard Pinguino pins for reference):
PIC18F2550 PIC18F4550 Pinguino IC name Pin mm8 Pin IC name Pinguino Reset MCLR/VPP/RE3 1 1 MCLR/VPP/RE3 Reset 13 RA0/AN0 2 A00 2 RA0/AN0 13 14 RA1/AN1 3 A01 3 RA1/AN1 14 15 RA2/AN2/VREF-/CVREF 4 A02 4 RA2/AN2/VREF-/CVREF 15 16 RA3/AN3/VREF+ 5 A03 5 RA3/AN3/VREF+ 16 Run RA4/T0CKI/C1OUT/RCV 6 6 RA4/T0CKI/C1OUT/RCV Run 17 RA5/AN4/SS/HLVDIN/C2OUT 7 A04 7 RA5/AN4/SS/HLVDIN/C2OUT 17 A05 8 RE0/AN5/CK1SPP 18 A06 9 RE1/AN6/CK2SPP 19 A07 10 RE2/AN7/OESPP 20 11 VDD Vdd (5V) Vss (GND) VSS 8 12 VSS Vss (GND) OSC1 OSC1/CLKI 9 13 OSC1/CLKI OSC1 OSC2 OSC2/CLKO/RA6 10 14 OSC2/CLKO/RA6 OSC2 10 RC0/T1OSO/T13CK 11 D12 15 RC0/T1OSO/T13CK 10 11 RC1/T1OSI/CCP2/UOE 12 D10 16 RC1/T1OSI/CCP2/UOE 11 12 RC2/CCP1 13 D11 17 RC2/CCP1/P1A 12 Vusb VUSB 14 18 VUSB Vusb D13 19 RD0/SPP0 21 D14 20 RD1/SPP1 22 D15 21 RD2/SPP2 23 D16 22 RD3/SPP3 24 USB- RC4/D-/VM 15 23 RC4/D-/VM USB- USB+ RC5/D+/VP 16 24 RC5/D+/VP USB+ 8 RC6/TX/CK 17 D01(TX) 25 RC6/TX/CK 8 9 RC7/RX/DT/SDO 18 D00(RX) 26 RC7/RX/DT/SDO 9 D17 27 RD4/SPP4 25 D18 28 RD5/SPP5/P1B 26 D19 29 RD6/SPP6/P1C 27 D20 30 RD7/SPP7/P1D 28 Vss (GND) VSS 19 31 VSS Vss (GND) Vdd (5V) VDD 20 32 VDD Vdd (5V) 0 RB0/AN12/INT0/FLT0/SDI/SDA 21 D02 33 RB0/AN12/INT0/FLT0/SDI/SDA 0 1 RB1/AN10/INT1/SCK/SCL 22 D03 34 RB1/AN10/INT1/SCK/SCL 1 2 RB2/AN8/INT2/VMO 23 D04 35 RB2/AN8/INT2/VMO 2 3 RB3/AN9/CCP2/VPO 24 D05 36 RB3/AN9/CCP2/VPO 3 4 RB4/AN11/KBI0 25 D06 37 RB4/AN11/KBI0/CSSPP 4 5 RB5/KBI1/PGM 26 D07 38 RB5/KBI1/PGM 5 6 RB6/KBI2/PGC 27 D08 39 RB6/KBI2/PGC 6 7 RB7/KBI3/PGD 28 D09 40 RB7/KBI3/PGD 7
Images