Charles L. Terra Ph.D.
USAF Veteran
The PCjr has become the little platform that users just cannot put on the shelf.
From the early days the folks have decided to upgrade and make better those features that
were intentionally left off  'the Peanut', or were just thought to not ever be needed by the
home user.   Some of these new  and old upgrades by the users have made 'the Peanut' that computer that the folks now cannot just call 'plain' !    
Below are just a few of the user designs and modifications that made live a little better for all of us.
JR-IDE Hard Drive / Memory / Clock
The most popular and exciting, in my opinion, has been the JR-IDE design by Alan Hightower.
This addon to the PCjr gives the popular Hard Drive addon, that in the day, only big $$$$ could buy this from OEM vendors.  Like myself the huge pricetag was always a barrier !
This new design answers three of the most popular PCjr needs, Hard Drive/Memory to a usable 640K/ and the badly needed Time Clock.

Shown below are two versions of the JR-IDE, the one on the Left is REV'C' that I have done a new layout using SMT parts and added a 2.5" drive interface to allow direct connect to the smaller footprint drives.
The unit on the Right is the REV'A' that has been reproduced by Texelec, a company in Texas
that is now producing the JR-IDE.  Kevin and his wife Sara produce many JR items and they can be found at their website  www.TEXELEC.com. 
( visit the FORUM for more detailed information on the JE-IDE board )
TANDYMOD BOARD - This board, designed also by Alan Hightower, allow the PCjr to run Tandy games that would otherwise produce the venetian blind effect.  More info on this can be found on Alans site
This board is my version of Alan's open source design
click the picture for more conversation on the forum.
PCSprint Speed Board - This board, originally designed Douglas A. Severson 11/85 was used on not only the PCjr but was aimed at the IBM PC group.  This board gives a significant increase in speed to your computer, in some cases a full 2X speed increase.  ( your mileage may vary )  The most common use was to include the popular NEC V20-10 chip.
This board is my SMT version of the design,
click the picture for more conversation on the forum.
3Flop Board - This board, designed me allows the user to have a full 3 Disk drives on the PCjr.
This attaches directly to the internal Floppy controller board with 6 wires attached for signals.
This board my design,
click the picture for more conversation on the forum.
PS2 to PCjr Key Board Adapter - This allows you to connect a standard PS2 Keyboard to your JR.
Note: The 3D Printed parts, these are available on the forum for download
PCjr Modem Slot Serial Port Board Adapter - This allows you to have a full blown COM1 on your JR.
The design has all standard control signals including the RI Ring Indicator that the JR has left off the
back port COM2.    
This board uses the onboard BAUD freq. to stay consistent with the JR design BAUD Rates.
This board is REV 'A', so note the 'jumper wire' fixes,  REV 'B' will have these fixes.
I have tested this board with a JR to JR connection using QMODEM, performing XMODEM Upload and Download at 2400 BAUD, each JR had this board installed.
'more to be added as time allows'