On March 30, 1951 The US Census Bureau receives the first UNIVAC I computer, the first commercial computer to attract widespread public attention. Although the Census Bureau began using it at the end of March it was not actually moved to the Census Bureau until a few months later. The UNIVAC was capable of completing 1,905 operations per second, which it stored on magnetic tape.
Source: https://www.computerhistory.org/tdih/march/30/#census-bureau-receives-univac-i-computer
On April 2, 1980 Microsoft Corporation announces the Z80 SoftCard–their first and (for many years) only hardware product–a microprocessor on a printed circuit board that plugged into the Apple II personal computer. It retailed for $349.00. The SoftCard allowed programs running under the CP/M operating system (included with the card, as was Microsoft BASIC) to run on the 6502-based Apple II with only minor modifications. In particular, the word processor WordStar was so popular that people bought the SoftCard and a companion “80-column card” just to run it.
Source: https://www.computerhistory.org/tdih/april/2/#microsoft-announces-softcard
On April 4, 1994 Marc Andreessen and Jim Clark found Mosaic Communications Corp., later renamed Netscape Communications Corp. Andreessen developed the software used for browsing the World Wide Web while working at the National Center for Supercomputing Applications (NCSA) at the University of Illinois. Clark co-founded high-performance computer maker Silicon Graphics Inc.
Source: https://www.computerhistory.org/tdih/april/4/#marc-andreessen-founds-netscape-with-jim-clark