Borland's Sidekick was an early Personal Information Manager (PIM) software application launched in 1983 under Philippe Kahn's leadership. It was notable for being a Terminate and Stay Resident (TSR) program, which enabled it to load into memory then return the computer to the DOS command prompt, allowing the user to load another application, but still activate SideKick using a hot key combination (by default: Ctrl-Alt). This approach allowed instantaneous task switching in the otherwise-single-tasking DOS. Although a text mode program, its window-based interface echoed that of the Apple Macintosh, and anticipated the eventual look of Microsoft Windows 2.0. It featured a personal calendar, text editor (with WordStar-like command interface), calculator, ASCII chart, and address book/phone dialer. According to the Borland IPO prospectus, SideKick sold more than one million copies in its first three years.
 DOS versions
Sidekick 1.0 included Calculator, Notepad, Appointment Calendar, Auto Dialer, ASCII Table and other tools.
 1.0 Plus
Sidekick 1.0 Plus included a broader selection of calculators (Business, Scientific, Programmer, Formula), a 9-file Notepad text editor, Appointment Book and Scheduler, a terminal communication tool and ASCII Table. In addition to variants on and enhancements to the 1.0 features, Plus included a 9-file Outliner, q file and directory manager, Clipboard, and supported Expanded Memory and a RAM disk. Control+Alt is the default shortcut to open sidekick 1.0 plus
Sidekick 2.0 was the last DOS version.
 Traveling Sidekick
 Sidekick for Windows
When Philippe Kahn left Borland in 1994 to found Starfish Software, he acquired all rights to Sidekick from Borland. Starfish's co-founder Sonia Lee Kahn designed the look and feel of Sidekick 95, which was launched simultaneously with Windows 95 with great success. In 1998 Philippe Kahn and Sonia Lee Kahn sold Starfish to Motorola for $325 Million in a private transaction. Software and trademark were sold to become a division of Motorola. Starfish was later bought by Nokia who discontinued the product, with SideKick 99 being the last version. T-Mobile USA, Inc. currently owns the Sidekick trademark portfolio.
Later versions of the program were made available for Windows, and were more along the lines of Microsoft Outlook, with the last versions of it supporting such features as a phone dialer, and support for syncing with Palm, Windows CE, and EPOC devices. These versions were less popular than the DOS versions, largely because the Windows environment itself provided most of the original version's key features: task switching and a collection of small utilities. It did however, include a monthly/yearly calendar and a world time map showing which parts of the world are currently in daylight or darkness. Up to eight different world cities (which could be edited) were displayed above and below the map.
Sidekick for Windows 1.0 was developed and released by Borland before Kahn left the company. It was designed for Windows 3.1 and included Calendar, To Do List, Contacts, a communication tool and a calculator. However, most of the design and file system came from the YourWay PIM software, purchased by Borland from Prisma Software in 1993. As the November 7, 1994 Info World noted, "Despite its name, the only connection between Sidekick for Windows 1.0 and the venerable Sidekick for DOS is that Borland International owns both programs. Sidekick for Windows is a combination of the calendaring code from Prisma Software Corp.'s Windows PIM YourWay (purchased by Borland last year) and a completely new interface developed by Borland." 
Sidekick 2.0 was also developed and initially released by Borland before the move to Starfish.
New/modified features included: - overlapping appointments in the Scheduler, - multiple contact files in the Address Book, - print layouts that enabled users to print to commercial day planner pages, - View-in-View, - Backup & Restore of user's files, - password protection.
Sidekick Deluxe added more than 40 content files for access to online information, Dashboard 3.0 for Windows, and the "Organized for Success" video. It was distributed in CD format.
 Sidekick 95
It included Write (a word processor with a spell check feature), EarthTime (a clock), Expense (record keeping tools), Reminder (scheduler), Phone Dialer (communication), Contact Manager and Calendar (with an added daily Almanac).
Sidekick 95 Deluxe added Dashboard 95, America Online software, 2 interactive organizational videos, over 40 useful content files called Sidekick Companions and electronic versions of the product manuals in Adobe Acrobat format.
 Starfish Internet Sidekick
Calendar tools added Activity view, daylight savings time support, web link support for contact files, Contact file synchronization over Sidekick 95.
Communications tool adds caller ID, phone dialer, integration with mail software. Spell check adds auto spell check option.
Calculator supports unit conversion.
New tools include Internet Scheduler, Expense reporter. Expense reporter includes date reporting, tax calculation, drag and drop receipts between folders.
 Sidekick 97
Calendar tools added ability to create web pages from Sidekick Calendar (via WP add-on).
Address tools added drag and drop, ability to create web pages from Sidekick Cardfiles (via WP add-on).
PDA sync is supported for Palm Pilot, via separate add-on.
World Clock supports European Daylight Savings time.
Sidekick Web Publisher compatibility is added via separate add-on.
 Sidekick 98
Calendar supports vCalendar, Outlook calendars.
Address tools support Outlook calendars.
Additional supported PDA sync include Franklin REX. Sync tool can now synchronize To do, Calls, Special Days, Appointments, and Contacts.
World clock added world map, Analog or Digital clock format.
In addition, features requiring separate add-ons in Sidekick 97 are now standard.
Long time users of Sidekick 98 report no difficulties continuing to use the program through subsequent iterations of Windows, up to and including Windows 7.
 Sidekick 99 (9.x)
Various tools found in Sidekick 98 are removed in this release, including dialer, back up & restore, calculator (including conversion tools, expense reporter), spell checker, web page generator, Internet scheduler. Address and calendar file format support were reduced, with Outlook support is now import-only.
 OS/2 version
 Mac version
A version was also available for the early models of the Apple Macintosh.
- Traveling Sidekick: A notebook that's easy to update
- InfoWorld Media Group, Inc. (7 November 1994). InfoWorld. InfoWorld Media Group, Inc. pp. 93–. ISSN 01996649. Retrieved 1 June 2012.
- Starfish Software Announces Sidekick 95 Deluxe; The first Windows 95 product offering direct access to America Online!
- Starfish Software Announces Corporate 10-User Value Paks for Sidekick 95 and Sidekick 2.0; Top-rated, best-selling organizers for Windows 95/NT and Windows 3.x users now available in new money-saving 10-packs
- InfoWorld Media Group, Inc. (14 November 1988). InfoWorld. InfoWorld Media Group, Inc. p. 5. ISSN 01996649. Retrieved 1 June 2012.
- InfoWorld Media Group, Inc. (9 September 1985). InfoWorld. InfoWorld Media Group, Inc. p. 27. ISSN 01996649. Retrieved 1 June 2012.