Built or owned by Omanis

"Having Become Aware Of Declining Portuguese Control, The Omani Raided Their Possessions On The East African Coast From 1652 Onwards And Repeated Attacks Were Launched Until 1696 When The Omani Arabs Besieged Fort Jesus, Mombasa, And Eventually Drove Out The Portuguese." (Ab Ev)

"In 1698, Zanzibar Came Under The Influence Of The Sultanate Of Oman. In 1832 Or 1840 (The Date Varies Among Sources), Said Bin Sultan, Sultan Of Muscat And Oman Moved His Capital From Muscat, Oman To Stone Town." (Wiki) And "The Old Fort, The Oldest Building In Stone Town, Was Built In 1699 By The Omanis"
See En.Wikipedia.Org

The Gereza Fort: The Present Form Of The Fort Is Of Typical Omani Forts.The Word Gereza Means Prison In Swahili, Possibly Indicating The Use Of The Fort As An Omani Slave Holding Building During The Late 18th Century To Late 19th Century (Wiki)
See En.Wikipedia.Org

"Lamu Invited Seyyid Said Ibn Sultan-Al-Busaidi, The Sultan Of Oman, To Install A Garrison To Protect The Town, Leading To The Construction Of The Fort, Which Was Completed In 1821. ... " (Ab Ev)